A CUP Full of Success: Manipulating ‘Unit Bias’ to Our Advantage

This concept and article were written in collaboration with Manchester-based climbing coach Adam from Underhang Climbing. My thanks go out to Adam for his help

It’s Christmas this week – or, if you’re reading any other time of the year, it’s only ever “just around the corner” – and a time for traditions. Everyone has their own traditions; be that stockings filled with gifts, wrapped presents under the tree, singing carols to neighbours, traditions are so varied. Some people may even enjoy themselves a Christmas Curry but that seems a bit Severe to me…

One of the more ubiquitous Christmas traditions is Christmas dinner. Whatever food you have matters not, the idea in the UK at least is simple: essentially, cook a typical Sunday roast but where you’d normally pick between one thing or another, at Christmas we simply have both.

The result is a plate so full of food that is often far more than we would usually consume. And yet, despite feeling full half way through, many of us will continue to eat through this, compelled to finish our plate; sometimes – and I speak from experience here – to the point of feeling ill. But why do we have this illogical compulsion? It turns out it’s all to do with a psychological phenomenon called ‘Unit Bias’.

Now other than being a nice little aside from our usual intense climbing training, why would I be filling a climbing website with waffle about the dangers of plenty from Christmas dinner? The reason is that Unit Bias affects us in all aspects of our life; including our climbing.

Defining Unit Bias

The term Unit Bias was originally coined by academic authors Geier, Rozin and Doros in 2006. Their paper, in Psychological Science, titled Unit bias: A new heuristic that helps explain the effect of portion size on food intake, proposed the idea that people have a tendency to finish single ‘units’ of food, irrespective of the size of the unit.

The website psychotricks defines it quite neatly for us:

The Unit Bias is a specific, powerful cognitive bias. It is defined as the irrational tendency to feel compelled to finish a given unit of consumption or task, regardless of whether that amount is necessary, desired, or optimal for our health, time, or well-being. It is a psychological phenomenon where an externally defined boundary — the “unit” — becomes a goal in and of itself, dictating behavior far beyond what rational decision-making would suggest.

Denys A (2025), The Unit Bias: Why We Can’t Stop Until It’s Finished, https://psychotricks.com/unit-bias/

This is why I was talking about Christmas dinner at the start. When researching Unit Bias, the typical example given is with food and with Christmas dinner often being the biggest meal of the year, it provides a great example of Unit Bias happening for real.

When we translate this into climbing, we quickly see that the compulsion is to get to the top of the climb at all costs. Trust me, when coaching, I often ask people to climb half a route, for a multitude of reasons: to warm up; to complete a practice lower for the belayer; for psychological safety; as part of a physical training routine; and so on.

Yet this can be quite challenging for people, especially when they’re ‘nearly there!’. Far too often, people simply push on and it’s all driven by this inherent unit bias.

Filling Your CUP

So if we’re beholden to this psychological phenomenon, what can we do about it? Yes, one could make the argument that by becoming consciously aware of a bias, we effectively release ourselves from it but perhaps there is another way. Perhaps we can even use this to our advantage.

Instead of trying to break away from the bias, why not lean into it by redefining the unit.

Redefining the Unit

Typically in climbing, one ‘unit’ will be the climb as a whole. From the bottom to the top, this is what we would usually class as one unit. But a climb isn’t (usually) as simple as that, we can break it into smaller components.

Even the very biggest climbs will be made up of pitches. Each pitch will consist of moving between protection, such as quickdraws on a sport climb. Even if we don’t have any protection to place, (we can think of boulder problems in this instance) can be broken down further into a series of moves.

With one client on a climb recently, even individual moves weren’t sufficient, being broken down further still, into both positions and the movements between them. Whichever way you choose to break down your climbing, all of these provide a potential new unit.

Now that we have smaller units, the unit bias can go nuts, compelling us to complete only the next unit but leaving the overall climb to a later date.

Introducing the CUP: Completed Unit Percentage

Now that we have smaller units, we can then begin to work out how many units we have achieved and how many are yet to be done. Effectively, we can see how many units we’ve completed.

For any given climb, this may seem fairly straightforward and we often hear climbers talk of having ‘done all the moves’ without claiming they have completed the route. This is exactly the same principle: breaking the climb down into smaller units.

However, there is an issue longer term. Indoor climbs, as an example, don’t tend to stay up that long and so knowing our progress over time can be difficult to track. We could look holistically but it’s not great. So how about we make this quantitative?

This leads us nicely to a concept developed between myself and Manchester-based coach Adam Underdown of Underhang Climbing that we called the Completed Unit Percentage. It involves a little maths but it’s not super complicated:

Okay so the silly diagram is a little unnecessary but you get the idea. So why is having a percentage useful?

Put simply, calculating our CUP for any given grade/style can allow us to track progress over time.

• We will have a CUP for any given grade, thus meaning we can track progress of our CUP for that grade across different times and different climbs
• Our CUP will not be affected by the length of the climb or the number of moves, being roughly even on any comparable climb
• A consistent CUP across climbs or the different styles at the same grade may indicate a well-rounded climber, with a highly variable CUP indicating a specific style preference
• For climbs at our flash grade, a ‘Full CUP’ should occur on the first climb

There is doubtless plenty more to be extrapolated from this principle. What we now have is a simple metric model that we can use to quantifiably track progress over time.

A Case Study Example

Adam has kindly agreed to provide some data to be used as a Case Study. Think of this as an example of the data happening for real.

On his given project – a blue 8a lead climb at Awesome Walls in Stockport – Adam tried the moves on second, unclipping as he went. In Adam’s words,

“So I had it as 71 moves for the 8a, 61 done first time or until rest when worked. 10 moves were multiple attempts (failed first time) which gave 85.9% CUP

I didn’t make a note of number of attempts I worked it just as either first time meant ✅ anything more than once was ❌”

Climb	Defined Unit	Total Moves	Completed Moves	CUP
Blue 8a	Individual moves	71	61	85.9%

What may have seemed, on the face of it, a remarkably distant challenge suddenly seems much closer. There will be challenges in linking these moves, yes, and it may be the case that over time, we need to readjust the units. But that’s a worry for another day. Right now, this gives useful data on how close we are to success.

What makes this even better is the short-lived nature of indoor climbs. So often, we have a short time frame to complete any project climb before it is stripped and replaced with another. In many respects, this gives us fresh challenges but when we’re attempting a top-end project, it’s not ideal. Having a CUP changes that.

Now we have a CUP for one climb, we can try different climbs of the same grade and see how close we are. Yes, it will fluctuate but it should provide some indication as to how close we are. For the mathematically inclined, we would then look to either reduce the standard deviation OR to focus on styles that maximise CUP (if that makes no sense to you, don’t worry about it).

Summary

We all hold within us inherent, unspoken biases that drive our behaviour. One such bias is known as ‘Unit Bias’ meaning the compulsion to finish things in distinct units. In climbing, this can often be problematic as our intention is often something other than reaching the top of the climb. Unit bias can prevent us from completing our training effectively, from perfecting our technique or can cause us to induce flash pump too early in the session.

But if we shift the unit, we don’t so much try and rid ourselves of this cognitive bias but instead, use it to our advantage. Changing our climb from ‘one unit of climb’ to multiple smaller units is a trick many climbers often employ but has hitherto not been linked with the related psychology.

Once we have smaller units, we can then compare the number completed units to the total number of units (most simply by calculating a percentage) to make something we’ve defined as a Completed Unit Percentage, with a nice acronym we’ve called a CUP.

Now we have a metric that we can use across multiple climbs, hereby giving us quite a lot of information that we can employ to help us to improve and track progress on our project climbs over time.

A Post Script Note

When I was writing this piece, I had a session coming up later in the day. I ended up leaving late and barely made the start of the session on time. The reason? I wanted to finish writing. In other words, I wanted to finish the ‘unit’ of text before leaving the house…

References/Further Reading

Denys A (2025), The Unit Bias: Why We Can’t Stop Until It’s Finished, https://psychotricks.com/unit-bias/

Geier, A. B., Rozin, P., & Doros, G. (2006). Unit bias: A new heuristic that helps explain the effect of portion size on food intake. Psychological Science, 17(6), 521–525. https://doi.org/10.1111/j.1467-9280.2006.01738.x