as strong as our weakest....

Bad Apple's comment is right on.

The quote was from TV series, Big Bang Theory.

Sheldon: Raj! What are you doing?

Raj: *raises coffee cup*

Sheldon: I don't think so! You've already had your allotted 6 ounces. The next bathroom break isn't until the Dennys near Bakersfield, which is approximately 2 and a half hours away. Remember people, we're only as strong as our weakest bladder.

Sheldon was telling Raj not to take another coffee as their next stop is 2.5 hours away. He didn't want to stop for toilet break during the ride.

Bladder who need to go to bathroom break between 2.5 hours duration=fault in somebody's(Raj) character of taking too much coffee,=a weak point=as strong as our weakest point.
It is called or named after the Greek hero Achilles=Achilles heel.
When Achilles was a small child,his mother held him below the surface of the river Styx to protect him against any injury. She held him by his heel,which therefore was not touching by the water of the Styx .Achilles died after being wounded by an arrow in the heel with broken tendon called Achillestendon.
As strong as our weakest point is called Achilles heel.