This question has probably created my philosophers through the ages that those deep thinkers would care to admit  

On a more practical note:

Handling rejection is part of life, and finding the means and many ways todo so is necessity. Meaning we all need to eventually learn to deal rejection, or it will surely stunt our personal development.

When it comes to love, learn that it's ok to lick your wounds, and then improve upon yourself, believe it or not, you can win greater affection from others as we grow in our attractiveness (note I didn't say looks alone).

When it comes to career and business, handling rejection is learning to have grit. Like the old saying goes 'When the going gets tough, the tough gets going'. Learn to be tough, if you must, then go learn sales (learn probabilities like for every 7 no your likelihood of getting 1 yes increase exponentially), learning to sell is one of the fastest way to learn how to brush off rejection like water off a duck's back. 

When it comes to social and personal side of life, follow this old adage, 'Those who mind, don't really matter, and those who really matter, they don't mind'

This is very general open ended question with no specifics, so I'm going to add that great motivation for dealing with rejection are plenty. No matter your unique circumstances, when look for them answers and you will surely find it. Peace and success be with you

Highest Regards,

Dj