If I gain, then someone else loses. Correct? On a very small scale, it's certainly true that if I gain, somebody else might lose. If I take away my brother's chocolate, then he will lose it, and will most probably not get anything comparable.

But on greater scale, say, nationally, if one person (e.g. successful start-up founder) makes a fortune, will this generally be bad for the other players? Or can it be beneficial (e.g. if the money is not saved up)? Does it entirely depend on the rich person's spending behavior?
I completely agree with denesp's answer, however I think you can make it even simpler.


  On a very small scale, it's certainly true that if I gain, somebody
  else might lose. If I take away my brother's chocolate, then he will
  lose it, and will most probably not get anything comparable.


OK, let's say I prefer chocolate to wine gums and my brother likes wine gums better than chocolate. Then taking his chocolate away and giving him my wine gums is good for both of us, so we both win and no one loses. So the answer is no.

You could even consider the extreme case in which your brother hates chocolate and you are doing him a favor by taking it. (Works not as well with chocolate, but you might think of recycling.)

In general these "trades" are called Pareto improvements.

But this is only one example, if you are interested in the subject, you might be interested in one of the following basic economic ideas:


Trade between two countries in which one of them is more efficient than the other: Ricardo's comparative advantage example
Your brother likes to give: altruism / warm glow (I really don't like the wiki page here, but was not able to find a decent non-scientific explanation of it.)
Or maybe other other-regarding preferences, for example fairness (your brother has a lot of chocolate and feels better if he gives you some): Theories of Fairness and Reciprocity (On page 3 is a brief "Non-technical summary" which might be interesting.)


As you can see there are many examples for a "win-win" situation and there are many many others, depending on the situation.