Investing is an activity only for true optimists.
You have to be a true optimist if you want the investment game to work out for you. Everybody can be an investor when all arrows are pointing upwards, and month after month new gains are made. That is the easiest part, everybody can do that part.

To quote Lou in Wall Street (the movie): “Remember there are no shortcuts. Quick buck artists come and go with every bull market but the steady players make it throughout the bear markets”.

Surviving the down turns is what investing is all about
The downturns are the hard part, and really what investing is all about. It is positioning the investments so that there is close to no chance of getting wiped out even how long the downturns lasts or how much loss the investment takes.

The person without a true positive character will lose faith at some point. When things start to look grim it is hard to stay positive, and people that gets easily depressed will not manage to keep feelings away from big losses and hearing negative news every day. Depressive people should not invest.