Life is too short to spend your precious time trying to convince a person who wants to live in gloom and doom otherwise. Give lifting that person your best shot, but don't hang around long enough for his/her bad attitude to pull you down. Instead, surround yourself with optimistic people.
Zig ZiglarIf you have the character to hang in there when its tough, you will develop or acquire every other characteristic necessary to WIN in the game of life.
Zig Ziglar