When people learn about feudalism often their reaction is to wonder how people put up with being starved, overworked, and largely powerless and without rights, for so long. Even more so when they learn that often the peasants defended the system as vigorously as the aristocrats, and were just a convinced of the right of the aristocrats to rule.
There are few social constructs that still exist which compare at all to the relationship of vassal and liege, but one understandable (albeit distant) comparison is to parental authority. If I try to tell you to go rake my yard, you would probably laugh at the idea. Obviously I have no authority with which to compel or entreat you to do that for me. Of course, if I had an eight-year-old son, I could tell him to do it.
Usually, the ability to make someone else do something comes from either a positive pressure (I can reward you for doing this), or a negative one (I can punish you for not doing it). But a parent's authority over his child is a fundamental and accepted societal construct that is neither of those, and fundamentally different.
Sure, you're thinking, of course a parent can punish a child. Don't rake the yard and I might send you to bed without supper. But how do I have the authority to send you to bed without supper? Again, by ordering you to go to bed without supper. I couldn't tell my next-door-neighbor to rake my yard, and if I did, I couldn't threaten to send him to bed without supper if he didn't. He'd just laugh. Now, if I held a gun to his head, then I have the authority of compulsion. It's the same thing if I threaten to reveal his affairs to his wife, or to withhold a promotion at the office, or any other application of real force. I have to take authority because I don't already have it.
As a child, did you ever stop to wonder, why do I have to do what my father tells me to do? Maybe you thought because you'd get spanked, but even letting yourself be spanked is an acknowledgement of that authority: you could run away from the spanking or cry for help, just as the next-door-neighbor's eight-year-old kid would do if your dad tried to spank him. No one would look kindly on someone whose attempts to spank his child went so far as to chase and capture him. Maybe because your dad is providing you food and a home? Sure, he might make that point, but if he withheld those things, society would look dimly on him.
In a way that's hard to put into words, but is very real, society simply accepts that it's part of our social structure that a parent has the authority to order his child around, and that the child does not have the right to resist that authority. The variations in how that authority is resisted and reinforced look very similar to how a boss deals with an employee, how a mugger deals with a victim, how a government agency deals with a constituent, or how a business deals with a customer. But in the case of a parent and a child, the authority is innate, it lives beneath all those expressions of authority, and they are expressions of, or symptoms of, that authority. In the other cases, the authority derives from those actions, and the authority is a consequence of them.
The fit isn't great but in a way the relationship of a serf to a liege is similar to that of a child to a parent, at least in that way of being fundamental, beyond question, and more the cause than the effect of the various visible incarnations of that authority in law and practice. Thinking about this is a good way to understand a serf's life and why it was usually accepted, just as most children never even ask whether their parents shouldn't have the right to set their bedtimes, just disagree with what time they choose to set.