Your very first one.
The first stock you bought.
Or the first mutual fund you invested in.
Maybe someone recommended it.
Maybe you bought it because you liked the company.
Maybe you had absolutely no idea what you were doing.
Whatever the reason, we’d love to hear it! 
If I recall right it was somewhere in 2012 or 2013 something like that first demat came with salary account on icici direct , PC jewellers ipo just came out I guess I saw it first stock in list saw how fast it’s growing and purchased 10 shares . And it started going down and I exited looking at losses .
Zero knowledge on markets or investing 