The only way to live a full life is to never stop living. The only way to never stop living is to always have something left to do. If you stop doing things, or run out of things to do then you're not living. So it's not that if you die with something left to do, you've not lived enough. The idea is if you die with nothing left to do, you've not lived enough. If you die having done 1 thing with nothing left to do, you've not lived. If you die having done 1,000 things with 1,000,000 things left to do, then you've lived a full life.
You must also stop doing everything sometimes and just listen to being understanding life. If you do 1 thing you truly understand in your life you will have lived a happy life, but if you do 1,000 things that you do not understand you will have a lived a meaningless life.