This is a human tendency to adhere to the by gones and thus we homo sapiens just don't understand the importance of Moving on. We stick to our past and forget to live the present for building up a greater and much brighter future than we actually deserve. By moving on I simply mean to "Move on!". We don't need to lament upon the past as it's not going to be such that you get the opportunity to relive it and write it again. It's already gone.

The Principle of moving on applies to each and every aspect of life. We actually need to master the art of moving on. If a student encounters a failure in examination, he is supposed to adhere to the principle of moving on rather than wondering about the failure. Moving on here is to analyse the reason for failure to make it a stepping stone towards a hard hitting success. 

Similarly principle of moving on applies to a person gone through breakup. It's actually say funny that a person after a breakup himself breaks and regrets about the ongoing. Here, the person is expected to move on and handle the situation with an ease. He need to understand that breakup is not the end, there might be some issues where the relationship could not stand true which actually in itself says that the relationship was actually fortituous.

So, these are major cases were people need to learn the art of moving on. But this is not the limit. Moving on is the principle which as earlier said is for every aspect of life.

Remember, Happeings gonna happen and thus "Let's Move On".