I was writing the same code block over and over for a month before I saw the problem
I was building a simple website for my friend's bakery and kept copying the same five lines of CSS to style each menu section. After about three weeks, I looked at my stylesheet and it was over 300 lines of basically the same thing. A guy in a YouTube tutorial said 'if you're copying, you should be making a class' and it clicked. Has anyone else had that 'duh' moment with CSS classes?