Hebrews 12:11 Now no chastening for the present seemeth to be joyous, but grievous: nevertheless afterward it yieldeth the peaceable fruit of righteousness unto them which are exercised thereby.

Notice the ending statement of this passage, "unto them which are exercised thereby". Previously in Hebrews 12:6-8, it was revealed that God only chastises those who are His adopted children. Now, notice that not all His children are excercised by His chastening, not all are affected and learn to be obedient. Some will be afflicted and live in calamity thier entire lives on earth. Even more sadly, only a few are able to see the affliction and calamity that so many live in, because they see themsleves as being righteous, and have no need for a physician to heal them.