know what it is to be/do something

know what it is to be (something)

To have thorough knowledge about or a lot of experience of being something. Don't stand there and act like you know what it is to be a soldier. You've never even been in combat. You should talk to Deborah. She certainly knows what it is to be a single mother running her own business.
See also: know, what
Farlex Dictionary of Idioms.

know what it is to be/do something

have personal experience of being/doing something: I know what it is to be a mother, so believe me when I say it is very hard work.
See also: know, something, what
Farlex Partner Idioms Dictionary
See also:
  • know what it is to be (something)
  • know (someone or something) through and through
  • know through and through
  • a world of
  • a world of (something)
  • put one through paces
  • plan out
  • put (something) through its paces
  • root out
  • think through