It seems like simple enough advice: always look on the bright side of life.
It also seems simple when people tell you to be realistic.
Hint: neither of these things is actually simple. And they really shouldn't be offered as competing alternatives.
We do ourselves a disservice when we frame things as either / or. EITHER find a bright side and make that all you see OR be realistic (and what... don't notice the up- and down-sides that are part of pretty much everything?).
Looking on the bright side is a discipline, the same way exercising is a discipline, or doing your best at work is a discipline. It takes time, and practice, and sometimes you need time off. Same with being realistic: sometimes reality is too bitter, sometimes it's too sweet. Sometimes your version of being realistic is balanced and accurate, sometimes it's skewed.
I've seen people get too caught up in looking on the bright side of a bad situation -- I've done that myself. For years, looking on the bright side meant that I didn't talk to anyone about my abusive stepmother, because I was too busy focusing on how the whole situation would be over in a couple more years when I left for college. I trained myself to pretend to see bright sides everywhere, even when I didn't.
But for the record, *only* looking on the bright side is a terrible idea. It's like looking away from things that scare you. Hint: it doesn't make them any less scary. Only confronting them - being realistic - can do that.
Looking back, I wish I had been more realistic about the situation I was in. I wish I had realized that my actual feelings were just as important as my desire to see the good side of a bad situation.
Realism and looking on the bright side don't work as alternatives. Use one and not the other, and you'll end up with a pretty unpleasant perspective on life. But when you find a balance between these two disciplines, these two ways of thinking, you can do remarkable things. You can start a business without risking your stability. You can see possibilities other people don't, and you can chart a path to achieve them. And you can get out of the situations that aren't worth staying in until those eventual bright sides come to be.