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 your watch is slow by just four minutes, that's not much - unless you've been warned that if you're even one minute late ever again you will be fired. Then four minutes make a big difference.
Zig Ziglar