Well, Lincoln might be right. But my belief comes mostly from my own experience. E.g. when I (more than twenty years ago) believed myself to be very happy with the man I had been living with for four years. Then suddenly (because of mainly financial reasons) I realized I had had enough of him. I saw everything in a new light. He loved me as much as he could love anyone else, but he loved his work better, and that wasn´t enough for me. As I hadn´t wanted to realize this, I had been determined to feel happy and didn´t want to see anything else until I couldn´t shut my eyes any longer.
When you´ve experienced something like that, it´s not easy to believe your own senses any more. But on the other hand believing it possible for other people to act in the same way.