How to know when to give up

One of my greatest failings is never knowing when to give up.  I often feel like that old Japanese soldier hiding out in some island jungle keeping watch, ready for battle long after the war was over. But other times I feel like the wimp who did not have the courage or energy to persevere. One time after heading out (pre-google and gps) only to feel lost and give up and come home only to discover I was one turn away from my goal, I asked my Dad why I had given up.  At the time his answer made no sense.  He said that I gave up becaiuse I could no longer see the land and feared the open sea.  I thought - huh I was in downtown Baltimore.  Now I think what he was saying was I was so focused on seeing the destination I failed to look around and recognize the clues along the way the landmarks the hint that I really was not lost at sea.
This has been a long summer.  My to- do list has gotten so long I have abandoned it and no new Fall list has appeared.  Usually when school starts and the evenings get cooler my nest feathering energy kicks in and projects start to poke up their heads but so far they haven't.  So here is the question have I given up because I can only see the end product and it looks too far away and I can't see any stopping off points so all I see is the huge expanse of sea between here and there or have I finally gotten smart and realized my limits.  Right now I just feel like I am caught in an eddy waiting for a wave or change in the tide.  Dad I need some advice.