It is said that people should accept themselves as they are instead of being dissatisfied with their own abilities.
Conclusion
If our goal is a society whose citizens are truly happy, then it's bad to say that people should accept themselves as they are rather than being dissatisfied by their abilities.
Evidence
Being truly happy requires that we're pursuing personal excellence or willing to undergo personal change.
Evaluate
This argument is just a complex way of saying,
This assumes that "if you do Y, you won't have Z".
Here the author is saying,
This must be assuming that .
Goal
Following the principle is accepting yourself rather than being dissatisfied with your abilities. So we're assuming, , as well as .