The encounter should happen in a settled area in a feudal state. The PCs should pass by a small homestead, with ragged crops and a slumping roof. Outside, the farmer, Petro Barisic, is holding onto a young heifer by a rope, and is engaged in a heated debate with an armored woman, Mirta Pavlovic, who wears the arms of the local lord on her tabard, and faces Petro with a stern and unflinching glare as she keeps her hand on the pommel of the sword on her belt.
Mirta is a woman-at-arms in the employ of the local lord who oversees this steading. She has demanded that Petro give up the heifer as a tithe to the lord's coffers. Petro rejects this, citing that he has little to his name, and his cow is getting old; he was hoping to raise the heifer to take her place so that he can provide butter and cheese for his family. However, Mirta insists that the lord's word is absolute. If Petro will not turn over the heifer by the next week, his family will be evicted from the land.
Most players will naturally see Petro as the victim in this situation, and will be inclined to take his side. His story is a truthful one. However, in a setting that believes in the divine right of the nobility, to contest the lord's demands - especially if the PCs are not of noble birth, or are foreigners - would be considered insubordination, and threaten the stability of the fief. The party might try to seek an audience with the lord in order to plead Petro's case, but it will likely not be easy to convince a noble that he should care for the plight of a single peasant, when he has armies to supply and treaties to negotiate with his neighbors, who may or may not be friendly. Petro's concerns are well beneath him.
Some parties might even try to incite open rebellion against the lord, but they should not expect to do so without facing stiff resistance, as the lord has more resources than they do. If they try to go up against the lord alone, they are up against whatever armies he can muster - to say nothing of any allies he might call upon from other fiefs and baronies. And even if his seat on the throne is threatened, the ensuing power vacuum might not be a step up - it might destabilize the region, or worse, lead to an even worse tyrant taking over.
The purpose of this encounter is not to punish the PCs for doing the right thing, and beat into the players' heads that everything they do is hopeless. It should still be theoretically possible to come out with an outcome that Petro will be satisfied by - perhaps they can sway the lord with careful rhetoric, or find a suitable substitute for the heifer, or even find a way to allow Petro to keep it under his master's nose. But by having such dilemmas come up in play and exploring the realistic consequences of how the PCs address them, you can give the players a firsthand look into how this isn't a world that will work the way their own life does, and prove that they shouldn't expect it to.