When one can bench press 250 pounds.
When you realize that life will always have burdens for you to carry. And you will always be able to deal with those and come out sane on the other side. Happiness is optional but you should pick it up...
When you acknowledge your weakness.
I use strength when i needed to use it. I don't like to waste this thing. Seriously, such things are hard to develop, sometimes takes many years and generates like small bottle. But when it is in charge, you show your strength.
The ability to laugh at yourself and maintain your self esteem.
* When you effectively help people who aren't in a position to help themselves.
* When you effectively overcome something/someone you are opposed to.
Physically, it is when you go to the gym. Mentally, it is when you discipline yourself to excel at some area. Spiritually, it is when you handle the misfortunes that life throws at you with grace and a balanced psyche.
I believe everyone is born with strength, though most may not realize it until they go through something that requires that strength to come through for them.