Rosy retrospection
We judge past events more positively than we do the present. Possibly caused by nostalgia.
Cause
Simplifications and exaggerations of memories (such as occurs in rosy retrospection) may make it easier for people's brains to store long-term memories, as removing details may reduce the burden of those memories on the brain.
Consequences
Some people theorize that it may in part serve a useful purpose in increasing self-esteem and a person's overall sense of well-being.