It did not even have to be a big win. It could be a small win like making it out the door to start your run or drawing something even though it sucks.
What matters is you showed up, you started the thing, and you finished it. If you keep going, if you keep putting in the effort, you'll eventually find that those small wins will have accumulated into bigger wins.
So, whenever you feel like you can't do something, think about a win that you have already accomplished and use that as motivation to keep moving forward!