Capitalists don't necessarily believe that those who work the most get wealthy. Those who create the most wealth get wealthy. The more value you create using your time, energy, brain power, etc. rewards you with a piece of that wealth. In a capitalist system, anyone is capable of working really hard, building a better mousetrap, contributing to society in a meaningful way, seeing a need and filling it, in short, supplying a demand. The greater the demand, the greater the value of what supplies it. Do that enough, spend your resources wisely, and follow the rules - you get wealthy. Just stay where you're comfortable, repeatedly make poor decisions, break the rules - you wind up broke, or worse.
It is a fact that in this society everyone is practically guaranteed a middle class lifestyle if they finished high school, didn't develop a drug or alcohol problem, didn't have a child out of wedlock, didn't get a criminal record, and work full time. Beyond that is up to one's imagination and willingness to work.
Capitalism is natural, virtuous, and dignifying. Socialism is manipulative, enslaving, degrading, and just downright wrong.