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 ZiglarIt's not what happens to you that determines how far you will go in life; it is how you handle what happens to you.
Zig ZiglarWhen someone we love is having difficulty and is giving us a bad time, it's better to explore the cause than to criticize the action.
Zig Ziglar