This happens to all of us at some point - maybe it's just a hard exercise, a lot of reps, or you have developed a bit of a mental block trying to hit a certain number.
That last one can be a real struggle, and I've been there many times.
A little mental trick might help you when stuck in that spot: change how you count!
I recently did a series of three exercises and realized that I counted each one differently.
I was doing a series of 7 of one hard exercise, 14 of a medium exercise, and 21 of the easiest exercise - and for not a single exercise, I started at one and counted my reps upward!
What the heck am I talking about? Read on!
Here are a few ways I've found to "trick" your brain when you're counting reps:
If you've begun to tie a certain number as being hard, say it's repping 4-5-6, try counting it as 6-5-4-3-2-1.
Now reps 3-2-1 should be the "hard" ones, but your brain associates those with easy reps, and you might find it a little bit easier to get all 6 in.
(I did this with my hardest exercise of 7 reps.)
Count up twice
If you're doing an even number of reps (let's use six again), you can count to half twice: 1-2-3-1-2-3.
Just like counting down, this helps avoid the association with "hard" reps, AND it seems like fewer reps if you're not actually counting up to a big number.
This works slick if you're doing really high reps or alternating sides (like with a crawl) - even if it's not necessarily a hard exercise, 20 reps sounds much higher than 10, twice.
(I did this with my medium exercise of 14 reps.)
Count a pyramid
If you're doing an odd number of reps (let's use 7), you can easily count up and down 1-2-3-4-3-2-1.
This works for the exact same reason as counting twice: it helps avoid the association with "hard" reps of 5-6-7 and seems like fewer reps if you're not counting up to a big number.
(This is what I did with my set of 21 reps.)
Now, mental tricks like this won't magically double your number of push-ups or pull-ups or whatever it is, but if you're stuck at a bit of a plateau and can't quite get past a specific number, then changing up your mental script might be just the breakthrough you need.
Give it a try, and let us know if it helps!