Tell someone they can't have something, and they tend to want it more

Psychologist Jack Brehm proposed in 1966 that people react to a threatened choice by wanting the restricted option more, not less — a 'reactance' that can make a ban backfire. It's the theory behind why forbidding a toy, a food, or an idea so often makes it more appealing, especially to children and teenagers.

— Jack W. Brehm, A Theory of Psychological Reactance — Academic Press, 1966