Trading is actually not for everyone, and trying with demo account can give you an idea of it it is for you or not without you loosing money in the process of discovery.
Right, trading isn't for everyone and those that can't take risk and accept to lose money when they start to trade. They're going to lose that much money on it. So, exchanges having the free accounts or demo accounts is a big thing for those that don't want to trade with real money yet. That is giving them the option to trade and test their strategies without having to burn their money.
It can be an indication that trading is not for you if you are finding it really difficult to understand the basics of how it works. But before you come to this conclusion, make sure that you have tried your best to understand trading and the dynamics, do not just quit trying to learn and understand at the first attempt.
If someone realizes that trading isn't for them, they have to recognize that as soon as possible for them to have no troubles at all. Because if they try hard and they're going to set aside their feelings, they'll save themselves from losing a lot of money. But no one is going to stop them from trying because trading is for everyone and everybody deserves to test themselves if they are for it or not.