People feel the pain of a loss twice as much as they enjoy the benefit of an equivalent gain. It's called loss aversion and it's one of the well-known psychological distortions that comprise behavioral economics. It's well-established by science and, in particular Daniel Kahneman and Amos Tversky who won a Nobel Prize for their work on Prospect Theory.
It turns out that losses and gains are not absolute, but depend on our perception instead. This means we can influence whether people perceive things as a gain or a loss by carefully controlling the way we phrase things. If your gas station, for example, offers a discount for paying cash, then you'll view that as a gain. If they charge a premium for paying by credit, you'll view that as a loss--even if the prices for cash or credit are the same!
Google Chrome leverages loss aversion to encourage people to sign in to the browser with a small message that says, "Not signed in to Chrome (You're missing out--sign in). Notice they don't say something like, "Sign in to Chrome to enjoy all of its features." That would position signing in as a gain and people would find it less compelling.
If you're not currently employing behavioral economics principles in your marketing, you're missing out. Spread the fire. GS