weesin I disagree with you because for 1 the quote doesn't say "can sometimes can", for 2 it is sorta true that "people with the loudest laughs and the biggest smiles have had the most painful past", and for 3 the author doesn't have to have researched about this they may have experienced it first-hand. By the way, there should be a comma because if you knew that the purpose of a comma is for you to take a pause, the quote is very reasonable and sounds a lot better with the comma, than without! When I first read this it touched me and I know dang well you probably couldn't do better, so while you are over here trying to be a critic you might as well criticize yourself.

"can sometimes can" doesn't make sense. And why would you say that "people with the loudest laughs, and the biggest smiles have the most painful past"? What research have you conducted to support this very generalized statement? Also, there shouldn't be a comma in that sentence. This quote poses very facile opinions