Wishful thinking is the formation of beliefs and making decisions according to what might be pleasing to imagine instead of by appealing to evidence, rationality or reality.
Wishful thinking might be the most underrated self-destructive force on the planet.
I think most people, when they hear the term "wishful thinking," they understand that it's a dangerous thing.
But has there been any great definition of it? Wikipedia's is too weighty to be thought of quickly.
Here's mine: Thinking an effect will or could happen without a cause.
When something isn't as good as you want in your life, it's tempting to just want things to get better. But, it's dangerous to entertain that notion blindly. Hope and faith are amazingly powerful and useful forces, but much better when combined with a bias for action and a little planning.
If you have an outcome you want -- don't just fantasize about the outcome. Think, "What could cause that?" And then start trying that stuff.