Why a bad thing? Sure, you end up lying to yourself, and you crash pretty hard when you are no longer able to sustain the illusion, but for that brief period of time when everything feels perfect life can be pretty good. It's a very invigorating situation, and it can lead to all sorts of good things.
A few years ago I found myself in a serious rut. Classic depression where everything feels wrong and there is no good side. One day I ran into a girl who had the most beautiful smile I'll ever see. I took her image and I filled with the soul of my perfect life-long mate. In less then a minute, I fell completely in love with her, and at the same time I forgot all about being depressed. Sure enough, the illusion didn't last, but it did show me that my happiness was something I had complete control over.
I'll probably never see her again, but I'll always remember the way her smile changed my life.