What is the DIY project you are proudest of finishing yourself

[Trinity49]

There is a genuinely specific satisfaction that comes from completing a DIY project yourself that simply does not compare to paying someone else to do the exact same job, even when the finished result might not be quite as polished as a professional could have managed, whether that is a piece of furniture built entirely from scratch, a room fully renovated over a series of weekends, or something far smaller and more modest that still required genuinely learning a completely new skill along the way.

What makes a DIY project genuinely memorable usually is not how impressive it looks to an outside observer, but how much was actually learned along the way, including all the mistakes made and corrected before finally getting it right. What is the DIY project you are proudest of finishing yourself, and what is the one thing you genuinely wish you had known before you actually started it?