Sometimes it takes a good fall ti really know where u stand
"know where you stand" generally refers to the relationships in ones life. Everyone loves you when you are on top, but it takes failure or at least faltering to find out who truly cares. If you matter to someone, they will be the one holding out the hand that pulls you back up when you fall.
It means that if you think you're all high and mighty, you might have to be suddenly brought back down to the bottom to know that you're not quite as great as you think you are.