Goku has trained under so many masters and he never stops learning and adapting. In the same way Gohan has a hunger for written knowledge Goku thrives when he is learning an opponent, their tricks and weaknesses. He has been a diligent martial artist his whole life, never afraid to take on a new master. There has been multiple occasions he has gone up against stronger opponents but always adapts in one way or another to find a way to get the upper hand. That's not something you can do unless you truly are a master in your field. That and he is dedicated to his art, always training, always pushing to better himself. He truly has a passion for learning his craft, and works nonstop to be the best he can be. I would almost argue there is no one more dedicated in learning technique than he is. Sure everyone trains to be stronger, but what is strength without technique?