Is it true that a short or small person can't beat a tall or big person in a fight?

The reason I ask this is because I was listening to someone on YouTube and they said size and height and weight is The only thing that really matter in a fight and that the only way to beat big people is to just gain weight and lift weights. If this is true then doesn't that mean that there is no hope of a... show more The reason I ask this is because I was listening to someone on YouTube and they said size and height and weight is The only thing that really matter in a fight and that the only way to beat big people is to just gain weight and lift weights. If this is true then doesn't that mean that there is no hope of a short or small person to beat a tall or big person? If so how? Because when people mention be in and out that's easier said then done. A big or tall person can just counter you. People also say get in on the inside but that's easier said then done. A tall person is hard to breach so how to you beat them? A big person is invincible so how do you beat them?
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