Yes the value is subjective but you consent to work for a given amount of time for a given amount of money. If someone agreed to give you 10$ and didn’t you could sue them. Also you are selling your labor to someone else. You are not entitled to the full value of the task unless that is what both parties agreed to.
It’s not easy. Selling your labor is more time and resource effective because you can’t be good at everything and you have specialized in certain skills. It allows for large scale corporation while still maintaining individual consent. Before there were civilizations people survived based on their own and a few other peoples labor around them.