But the most important thing before going to play and gamble is the need for real money and or something of value such as an asset to be at stake so that it can be called gambling in its entirety because gambling without something at stake is rather difficult to call it gambling. 
What is certain is that if you don't use money, there is no challenge that people will feel because they can place bets with large amounts of demo money. Gamblers are looking for challenges like that, so it makes them come back for more. But if it's just for fun, they can play without using real money. Well, everyone must desire to gamble or just play without using money or anything that can excite them.