Let's imagine that one day in Phys Ed class you're playing volleyball and you twist your ankle while you dive for a save. Everything feels all right, but you wake up the next morning with a giant bruise, a swollen ankle and a lot of pain. What would you do? Most likely you'd go to the doctor's. In fact, if you didn't go, but kept limping around insisting you were all right, your friends would probably drag you there themselves.
We know when it's important to get professional help with our physical ailments. It just makes sense to us. But as a society we have problem seeking professional help with our mental health. We often label people with mental illnesses as 'crazy,' and think that if we can't take care of issues that affect our mental health (like stress, anger, or loss) then we must be weak.