Persistense is the ability to maintain action regardless of your feelings. You press on even when you feel like quitting.
When you work on your big goal, your motivation will wax and wane like waves hitting the shore. Sometimes you'll feel motivated, sometimes you won't. But it's not your motivation that will produce results - it's your actions! Persistense allows you to to keep taking action even when you don't feel motivated to do so, and thereafter you keep accumulating results.
Persistense will ultimately provide it's own motivation. If you simply keep taking action, you'll eventually get results, and your results will be very motivating.
Does this mean you should always persist and never give up? Certainly not. Sometimes giving up is clearly the best option.
So how do you know when to press on vs. when to give up?
Just ask yourself -
Is my plan still correct? if not, then update your plan. Is your goal still correct? If not, then update or abandon your goal.
Know there is no honor in clingling to a goal that no longer inspires you.