Some inspirational quotes to live by are "Happiness is found when you stop comparing yourself to others" and "Beauty is about being comfortable in your own skin." The latter is said by Emmy-award winning TV host Ellen DeGeneres.
In 2015, in The 1989 World Tour, American singer/songwriter Taylor Swift always opened her "Clean" performance by an inspirational speech. She said in the opening night of her concert in Tokyo Dome, Japan: "You are not your mistakes." A video of Swift making the speech was posted on Facebook and as of December 2015, it has gathered over 14 million views and 250,000 shares.
Regarding why people should stop comparing themselves to others, apparently judging one's achievements against other successful people often leads to low self-esteem. In life, there are always people that are subjectively doing "better,” so if a person judge himself by those standards, he is never going to feel good about himself. It can lead into a downward spiral of giving up on goals because he would feel like he can never measure up.
On the other hand, if a person usually feels superior to others, he is likely to be ignoring the areas that needs improving. Last but not least, comparisons don’t take into account the many differences individuals may encounter. People encounter different obstacles on their path to success, so a person cannot truly judge his own worth by looking at someone leading a completely different life than his own. Ultimately, the only real measurement of success and happiness is himself, so letting go of comparisons can help him define success and happiness in his own way.