Persistence or Insistence?

I realized that persistence can really get you what you want in the end. But when does persisting need to stop? When does persistence just become insistence?

A friend has been persisting on a goal, and it looks like he might get what he wants. I, on the other hand, have been persisting on my own goal and yet my efforts (??) seem futile.

I am quite stubborn and am hopelessly optimistic -- and with reason, too. I have had so many experiences in the past where I persisted at a goal regardless of discouragement and negative feedback from people around me, yet I end up succeeding in the end. It is this "track record" that makes me even more stubborn and persistent now no matter how absurd it's starting to seem.

I usually follow my gut feel, which is usually right. However, in this instance, I wonder if I'm being unreasonable, and maybe for once I should just let go of this goal and be more realistic instead of telling myself that if I try hard enough then it might come to fruition eventually.

I have a friend who's like as old as my dad and I admire him a lot for his wisdom, wisdom I can only wish I already have. I tend to go by the book on almost everything. For me, it's either black or white. I guess only experiences teach wisdom, and only mistakes can teach us how to do things better. Unfortunately,this comes with age, and with my "sheltred" life, it won't be easy.

That said, I wish I had the wisdom to discern when to stop aiming for something. Until then, though, I guess I'll just have to do things the way I know how -- that is, to keep trying till I succeed or till I get too tired to go on :P