Found this on Quora
People always want what they can’t have.
Here are three reasons why this is so:
1. Heightened attention: When something is hard to get (or forbidden) you immediately pay more attention to it. Notice that when you are on a restricted diet, you sometimes get too focused on what you “can’t” eat. This heightened attention — which can escalate into obsession — makes the forbidden food seem very important. Your inner brat takes advantage of this, and tries to convince you that you MUST have that chocolate or pizza.
2. Perceived scarcity: When something is scarce or in short supply, its perceived value increases. You want it more because you think other people also want it. If you’ve ever bid at auctions or on eBay, you know the experience of that last-minute excitement as you watch the bids spiral upward. The more people who bid, the more you’re willing to pay for the item. Your inner brat wants it at any price.
3. “Psychological Reactance”: People don’t like to be told they can’t have or can’t do something. It’s related to not wanting to be controlled by others, especially if the situation feels unfair or arbitrary. The “reactance” is both emotional and behavioral.
The emotional part is your inner brat saying, “Oh yeah? I can’t have what I want? Just try to stop me!”
The behavioral component is what you do about it, which usually involves some type of rebellious reaction. You see this with teenagers whose parents have forbidden them to date certain people. Reactance also explains why a “Wet Paint” sign always invites unwanted fingerprints on the newly painted surface.
Next time you don’t get what you want, ask yourself whether one of the above factors has influenced your desire. If so, let go of the pursuit. Your inner brat won’t be happy, but ultimately (in the words of the Rolling Stones,) you “might just find [that] you get what you need.”