Sorry, I didn't want a misleading title.

For example you message a girl who sees your message but doesn't answer. (or she knows you're going to message her but ignores you.) OR she rejects you by saying she's busy (but "sometime later" she might be available).

How do you know when to stop pursuing her? There are a lot of girls who would like to see the effort before they give in -- and sometimes I think they're right: putting in effort and pursuing may indicate serious intentions. But on the other hand... how do you know the 'frontier' -- I mean how do you stop being needy and "let go" without embarassing yourself? In the above example, do you message her 2-3 times more, or do you keep on asking her out?