A time to give up???!!

Today I was reading a little in Ecclesiastes and this verse popped out and got me. It's found in Ecclesiastes 3:6 and says:

A time to search and a time to give up
A time to keep and a time to throw

A time to give up?!!! WTF this isn't even in my vocabulary!  I have worked so hard for everything I have.  I don't EVER give up. It's one of the best and worst things about me.  Maybe it's something I need to learn.  I think there is a fine balance to be had.  I also think some people are wired to to give up easier than other.  So how do you know when to give up?  My best assertion is that it's time to give up when you have spent more time on doing something or seeking something that something is worth to you.  For this reason it's really variable depending on what you're looking for, how valuable or replaceable it is and how long it will take you to acquire its replacement.  Some things are irreplaceable and that further complicates matter.  I am going to try to be more conscious of the time I spend on things that I should give up on.