What is the meaning of [One must draw the line somewhere]

To draw the line is to lay down a definite limit of action beyond which one
refuses to go. The decision depends on ourselves, but it must be taken sooner
or later.

> ‘My wife and I were getting so many invitations to dinner parties that we
never had an evening to ourselves. We had to draw the line somewhere, so now
we turn down all invitations for Tuesdays and Thursdays.’