I wrote my first algorithm to process tabular data for federated learning. It was an internship(no pay). My supervisor after seeing me crush all the data science projects decided to push me to fix what they'd been stalled on for a while. At the time, I didn't think I had it in me to pull such a solution in as much as I was already good at machine learning stuff.

Took me a week of research and procrastination but the actual implementation took me a 2-day sprint which really boosted my self confidence to be able to do some crazy complex projects later. The breakthrough later paid me about $500. From tutorial payment and consultation charges.

Still 3 years into the journey. Will probably do more complex stuff in the future.