What Are Your Greatest One-Shot Life Improvements?

A LessWrong question post crowd-sourcing what Xu calls "one-shot solutions": a single change you make once that permanently improves your life (e.g., moving your bathroom scale to the doorway so you weigh yourself every day without thinking about it). The post has dozens of answers covering keyboard shortcuts, household reorganisation, diet swaps, financial automation, and dental/medical interventions; the framing is that many problems aren't hard to solve, you just have to notice the solution exists.