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 ZiglarWhen you are tough on yourself, life is inevitably easy. When you are easy on yourself, life will be inevitably difficult.
Zig Ziglar