system
A chat on subreddit /r/wallstreetbets
human
Most employees will sell all their vested stock on IPO lockup expiration day. They usually have more stock vesting so they aren't totally F'ed if it keeps going up.

gpt
True, gotta keep Uncle Sam from getting all those taxes. 
  
 Tbh it would hard, to not cash all of them right away (if fully vested) especially if the company is volatile, no matter on how much you gotta pay the tax man.