Robber barons who felt like taking what they pleased soon found themselves and their families stripped of their titles by their betters. No one really felt like giving their liege lords a justifiable excuse to take their lands from their clans, so it provided a decent incentive to not be a tyrannical bastard, assuming you were of that persuasion to begin with. Although sometimes the system, as good as it was for higher lords and as much as it tried to mitigate the shittiness for the commoners, was rarely a pleasurable experience for petty lords. Like, say, barons for example.