it's one thing to (do something), it's another to (do something else)

it's one thing to (do something), it's another to (do something else)

While it may be acceptable to do something, that does not make it acceptable to do something that is much more extreme or complicated than the first thing. It's one thing asking us to stay an extra hour each evening to finish a project, but it's quite another to demand we work every weekend without overtime or else risk being fired. It's one thing to express your affection for someone you've started dating. It's another to bombard them with declarations of love after just a few days.
See also: another, one, something, thing
Farlex Dictionary of Idioms.

it’s ˌone thing to do ˈA, it’s (quite) aˌnother (thing) to do ˈB

,

A is ˈone thing, B is (quite) aˈnother

used for saying that you find the first thing acceptable or possible but the second thing definitely unacceptable or impossible: It’s one thing to write a short article; it’s quite another to write a whole book on the subject. Romance is one thing, marriage is quite another.
See also: another, one, thing
Farlex Partner Idioms Dictionary
See also:
  • (something) is one thing, (something else) is (quite) another
  • it's one thing to (do sth), it's another thing to (do sth else)
  • it's one thing to (do sth), it's quite another to (do sth else)
  • it's one thing to do A, it's another to do B
  • koshe
  • something else entirely
  • be in step (with someone or something)
  • get (someone or something) into shape
  • get into shape
  • knock (someone or something) into shape