The difference between admiration and resentment is fairness.
If someone has a better life than we do, and they deserve it more than we do, we admire them. If someone has a better life than we do, and they don’t deserve it any more than we do, then we resent them (or we resent the system, or the fates).
We can tolerate inequality when it is earned. We can even tolerate it to some degree when it is produced by luck. But when it’s produced by a system that favors some over others for no obvious merit-based reason, then we begin to seethe with the corrosive kind of envy. And we begin to dream of toppling the system.