But here’s what Cialdini found: the return favor is often dramatically larger than the original one. A 50-cent sample can trigger a €50 purchase. A free coffee might land a million-dollar contract. Is this manipulation? Maybe. But it's also deeply human.

When people discovered The SUB (a little home draught machine for beer) was made by Heineken, their perception shifted. Some loved it more because “Hey, it’s Heineken — they know beer!” Others instantly disliked it because “You know what they should do? Start making real beer.”

That’s crazy right? Same product, different reactions based on one detail.