I was tasked to add OpenOffice's hyphenation lib to our software at work back in 2010 when I was a junior dev. I had to read the paper and the C code/documentation to understand how it works but got stuck in one particular function.

It was such an obscure thing (compare to web dev stuffs) that I couldn't find anything on Google.

Had no choice but to ask on Stackoverflow and expected no answers. To my surprise, I got a legit answer from someone knowledgable, and it absolutely solve my problem at the time. (The function has to do with the German language, which was why I didn't understand the documentation)

It was a fond memory of the site for me.