(something) is one thing, (something else) is (quite) another

(something) is one thing, (something else) is (quite) another

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. Asking us to stay an extra hour each evening to finish a project is one thing, but demanding we work every weekend without overtime pay or else risk being fired is quite another. Expressing your affection for someone you've started dating is one thing; bombarding them with declarations of love after just a few days is another.See also: another, one

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