Whatever you are going through right now, no matter how horrible or frustrating it may be, there will always be someone else who has it worse. This you can be sure.
“Cast your eyes upon the great company of people you know, or do not know…everywhere you will find those who have suffered greater losses than you.” – Seneca
Even in your worst moment, there is someone who would gladly trade about anything to experience your suffering instead of theirs. That is not to say your pain is not real, invalidated, or that you have no right to your feelings. You absolutely do! But remember this: On the whole, you have experienced many more blessings than curses.
It is just difficult to keep this perspective while in the moment. But try if you can. Practice it while things are not so bad so that you will be better at remembering it when real tragedy does come your way.