Study any martial art (preferably one where you can spar) and you'll forever understand the meaning of ego. You show up, do drills/padwork, think you're making progress and then spar someone who beats you up. You do the same thing the next day, and the next, and the next. Eventually you improve and make progress because you're training so hard. But there's always that one guy you can't beat, and that new kid whose far beyond his years in talent. Coach is also now telling you your making mistakes on things you thought you put behind you, and its frustrating the hell out of you that you can't fix it fast enough. Your technique isn't up to par, your cardio is garbage because you had pizza and beer, and your training partners are running circles around you.
That's when you realize you know nothing, that even after these years of training and experience, you feel even less knowledgeable about the art than when you began. Depressed about your progress, you figure you have two options to deal with it: 1) quit... or 2) keep showing up. But by now, you love it too much and its become apart of your life, so quitting isn't an option. All that's left to do then is to continue showing up.
Eventually, the ego is beaten out of you from every failure/loss/disappointment in your daily training. You've tapped out to newer people, younger people, smaller/bigger/"dumber" people that it doesn't even shock you to perform poorly against a total beginner. From here, self-realization naturally guides you into a more focused path for self-improvement. What you want to achieve today is far different from what you thought you'd wanted out of martial arts in the beginning. Telling apart someone who thinks they "know", and someone who truly "knows", is far easier. You'll realize how little you know, as it will humble you. But hopefully you'll come to peace with who you are, and realize what it takes to be where you want to be.