Why do I suck at climbing some days?
Very often, climbers can experience weak days. These are days that they just feel as if they have no power and no energy to climb at the level they normally can. This is not unique to climbing, or to sports in general. It's just part of being human.
Some people feel this way due to fatigue, they may be pushing their body too much and not giving it the amount of rest it needs. This can cause you to just feel very sluggish and weak, resulting in a weak climbing day when you just don't have the energy to climb, or don't have the power to do moves you normally would be able to.
Distractions are also very common. People who are distracted by something and who are not focused on the climbing session can very easily feel this in their climbing. They will just not be in the zone, not be focused on what they are doing, and this can very easily result in not being able to climb at the level you are used to climbing at.
Some climbers may also face medical issues. Depression, for example, is one that can really affect your climbing, and your whole life in general. If you notice that you are just not able to climb and don't feel the way you normally feel, and this feeling lasts, it is highly advised to go see a specialist as this may be something more serious than just an off day.
Having weak climbing days can also be a result of your eating habits. Some people feel very weak and shaky if they don't eat a little bit before their climbing session. Others, on the other hand, may feel the opposite, and eating even a small meal an hour before their climbing session could make them just feel heavy and tired.
You could try remembering or writing down each time this happens and how you were feeling, or what you ate before, or any other important details you may have, and then to try and find a common element shared by these days. This could be a great way to find the cause, and eventually, a solution.