I remember working through Brian Harvey's SICP lecture notes and HWs a couple of years ago. Each Homework had one harder exercise labeled "Extra for Experts" which I later found out was standard in a lot of UC Berkeley courses.

The recursion HW was really fun so I took it upon my self to never look up the answer to the Extra exercise no matter how long it took me to solve it. The problem was to re-implement the recursive function of the last exercise using only lambda functions. I wrestled with it for hours, then gave up, then got back to it days later before I finally cracked it.

Later that day I googled the question to see better/ more elegant solutions and found out about this thing called Y combinator, I googled it to know more but everywhere I look I see this company called Ycombinator. Down the rabbit hole I went and 27 PG essays, 230 HN hrs and 2 years later, here am I

Good times :)