When to sell?

New to crypto; excited about Bitcoin. I fucked up and sold a chunk of my stocks instead of BUYING as Bitcoin crashed in March 2020.

Market crashes, people sell.

Market skyrockets, people... sell?

If Bitcoin hits the projected $100k in 2021 (correct me if wrong), how long after would it come tumbling down?

I identify political and economic events that correlate with bitcoins value; what other factors contribute?

Basically, when do you buy when do you sell? Big question I know.

Thanks for your patience and insight!