First of all, not fighting means you’ve given up. Period.
First life lesson that we all should know by now is that life has no absolute certainties. Secondly, the downswings of life are inevitable. In one lifetime, we will feel all kinds of emotions; love/hate or happiness/sadness. We will shift between our ups and downs but days of darkness are those that will make us stronger and expand our understanding on life. In addition, our darker days contribute to us evolving and growing as a passenger in life. Whatever it might have been or still is, our misfortunes prepare us for what’s to come – good or bad. For that reason and many more, we fight even if there is more to come.