For those who are having difficulty maintaining a certain number of push-ups in each set, such as doing 15 push-ups each in 5 sets, when you are doing your push-up, do not be in a rush to complete your push-up. Always take a minimum of 20 minutes to rest before you can start another set so that you will have enough strength to do the same number of push-ups you did in your first set.
This is very important, we don't have to take the challenge as a military work. Yes we have to be committed to the challenge, but it shouldn't come to you as a burden. If you make it looks like a burden to you, you won't enjoy the challenge. You should spread out your sets, so don't be much of a stress to you. Moreover nobody is punishing you for not doing all sets at a stretch.