Final answer:
The principle indicating that people perceive their romantic relationships as better than others' is self-enhancement, a form of self-serving bias that maintains a positive self-concept.
Step-by-step explanation:
The principle that has been found through research indicating that people often perceive their own romantic relationships as being better than others' is known as self-enhancement. This tendency is a form of self-serving bias, where individuals evaluate themselves in a manner that is flattering or favorable, especially when comparing their relationships to those of others. The phenomenon helps maintain a positive self-concept and contributes to an individual's overall self-esteem. Such behavior is a natural part of the human tendency to view one’s own intimate connections as superior, illustrating a biased approach in social comparison processes concerning relationships.