The first time I was able to create a solution to a problem I had.

It wasn't some super-difficult problem, but the code worked, and I got my first jolt of satisfaction in a long, long time. And more importantly, I wrote it with my own two hands.

It was a Slack slash command and it takes a task number, sends it my server that creates a query for our Redmine, formats the returned data and posts it back to Slack. It only took a few hours to implement (mostly because I was unfamiliar with Slack's API), and while only a few people uses it frequently, I still get a small amount of satisfaction whenever someone mentions it.