When parents are sad to see their little toddler become a teen and tell us how sad they are to see them grow up and go to school, count the days you have watched them since they started nursery or school. Remember the hours and minutes you packed the lunches, sorted out homework and bought that uniform.
Now try to add it up. Well, it doesn't matter what the final total is, it's time you spent with your child. Time I never had and never will. This is sadness.
So when you think you are sad, be joyful for what your time, because I can tell you what it's like to be heartbroken.