That moment when your elegant university CS theories get absolutely demolished by industry reality. The top shows a pristine school bus (your theoretical knowledge) calmly sitting on tracks, while the bottom shows that same bus getting obliterated by the freight train of real-world development.
Seven years into my career and I'm still waiting to implement that perfect red-black tree I spent weeks studying. Meanwhile, I'm knee-deep in legacy code written by someone who clearly thought variable naming was optional and comments were for the weak.