"It takes more courage to examine the dark corners of your own soul than it does for a soldier to fight on a battlefield." - W. B. Yates Anyone can be physically strong, but being physically strong doesn't necessarily mean that we are mentally strong.
To be mentally strong, one needs to have an inner courage. This courage isn't blindly running foolhearted at something. Rather it is standing up to the darkness that inhabits our inner souls despite the pain or fear that it elicits.
Yates' quote is so apropos to budo and because true budo is really just the journey that one undertakes to develop themselves.
It's like the cave scene in Empire Strikes Back. Yoda says, “That place… is strong with the dark side of the Force. A domain of evil it is. In you must go." Luke asks, "What’s in there?" Yoda replies, "Only what you take with you.”
When push comes to shove, what we do shows our true inner character. To be the people that we want to become, we need to have courage and be brave. Courage is the inner attitude or strength and bravery is what it looks like on the outside.
The only true strength is the strength to keep on going despite the odds and that is the definition of courage.