Learning Solidity. I've been in crypto space for a long time, always wanted to learn Solidity to write contracts, but always postponed. Played with some toy code in the past years and that was it.
Recently got back in the scene and saw how many new business opportunities it opens and how financially feasible they are now I hate myself for not going more serious in crypto and Solidity in the past years.
Anyway, later is better than never. (Which applies to pretty much everything in life)