The world breaks everyone, and afterward, some are strong at the broken places.
I think some things hurt you on such a deep fundamental level that one cannot help but be scarred by them. I think that people develop coping mechanisms to deal with those things, and while they may be happy and find joy in life, the scar always remains. It’s a scar—your emotional skin isn’t perfect anymore. When you touch it you may have phantom pain—no matter how joyful your life is.