This bothers her and plants seeds of doubt in her mind about whether she made the right choice. Being confronted by jarring feelings of self-doubt can be quite debilitating and painful.
This can happen to anyone, as there will always be someone superior in one or more dimensions to the person we are dating.
The good news is that for the vast majority of people, these are fleeting thoughts and pass into the wind in short order. We recognize that no one is perfect and that it is unrealistic to so easily lose heart in a relationship.
If you are struggling with this, it is important that you think clearly and understand the math. The person you saw in the store or on the street is irrelevant. If you had your chances all over, the likelihood is that you would find that you are not compatible and have little in common.
You would be giving up on someone with whom you have a 90% chance of a successful and happy marriage to pursue an interest in someone with whom you most likely have no more than a 5% chance of the same – maybe lower. The numbers just do not add up. You are just playing roulette with your life.