A failed knight who became the strongest

I worked so hard, just for them to say I was unworthy to be a knight, I couldn’t accept this, but I couldn’t do anything since I was too weak, as they say the strong rule over the weak, but being a knight was the only I was good at, I became a mercenary only to be betrayed for a piece of treasure that was worthless, stuck in a cave for 10 years all I could do was train, train until I could walk out