Depends on situation really, and the way you approach the "problem". At some points you should accept that and get over it, if you see, that your trying to get attention from your crush makes her/him uncomfortable in a bad way and you really care for that persons well being. On other times you can try to show to the person that you are worth the time, but of course you have to know how to do that, can't got overboard. Its REALLY long process, had tried that myself.
Like there is saying: If you love something - let go. I don't believe in that. If you love something you should reach out. Let go sounds like just give up if something doesn't go as you like. But as I say, it depends really on the situation and your ability to analyse situation and make the right choice.