Playtesting is an extremely core aspect of making a game. Whether it be playing through what you just programmed, or it be watching someone play your game— seeing how they react, if they find any bugs—or someone playing your game on their own time and reporting back to you with their own curated notes, you need to test the things you make. There have been times I've not playtested things, and major bugs show up during YouTube let's plays of the games I've developed, publicizing my error indefinitely. The lesson I've learned, and what I want to bestow upon any new or upcoming video game developers, is that you will fuck up your code, and no matter what, you should never assume that because theoretically something should work, that it will in practice. And the only way to know something will work in practice is to playtest your game. So, do that. Try to break your game. It's tedious but it's worth it. Let your friends and family try your game; let them try to break your game. Take notes and ask them if you can record their playsession in case you need to recreate any bugs. It might be scary, but you'll learn a lot.