What is the most important lesson you ever learned

The most important thing I ever learned was that I am the only person that can make me happy.

After being married for 26 years and having three children I thought that they(my husband and sons) could make me happy by returning my affection.  This is not true.  They did return my love but not the way I gave it out and that ticked me off.  I wanted them to want the same things for them that I wanted.  I wanted my boys to grow up, be happy and successful at whatever they chose to do.  I wanted them to appreciate me and the things that I thought were important. 
What I found out was that there was nothing they could do if I was not personally happy with  myself.

Why is this the most important lesson:

It is the most important lesson because at the end of the day I have to look myself in the mirror and ask if I have done my best.  If I did not do my best than what can I do tomorrow to make it a successful day.  No one else is responsible for my happiness and no one can do anything that will make me happy.  If I am not happy it is a choice I have made - sometimes not consciously but a choice all the same.