Realists tend to suffer with depression whilst the person with positive 'illusions' does very well. It has to do with the way our humanity works. To participate in life we need dreams and hopes for the future. Why get out of the bed unless we thought we could make a difference today, unless we thought we could do some good somewhere?
Trusting that there's a purpose to everything, a loving purpose gives us energy and creativity, our minds open up to finding some good somewhere. Sure, there're negative situations and cruelty but everything can be turned around once we have energy and vision of something better around the corner.
Having dreams doesn't mean that we sit around waiting all day for things to work out, no, it means getting off our bum and do something which brings us closer to the fulfilment of our dream. Do something to improve a bad situation.
The person who believes in calling forth a better world for themselves and everyone else will see possibility that others don't see, will think outside the box while the rest of us are walking around in circles. That person will inspire us to give something another go, or leave something or someone behind in order to make things better.
The more each one of us believes that there's something better around the corner and apply ourselves to doing whatever it takes to get around the corner, the more wonderful the world becomes to all of us. Even if that something better is simply a deeper awareness of that inner love and goodness that exist within everyone including oneself.