You aren't gonna need it

You Aren't Gonna Need It (YAGNI) means that when you're writing code, you should only include things that you actually need as you’re writing it. It's a way of making sure that you don't write too much code. Imagine you're playing with a lego set - if you don't need the lego pieces immediately, you don't take them out of the box. Trying to make a spaceship with a lot of extra pieces that you don't need right now doesn't make the spaceship look any better. The same thing is true in code - writing extra stuff that you don't need can make it much harder to understand the code and find mistakes.