A simple question with a simple answer or is the answer really that simple?
You could say that strength is simply the ability to lift a heavyweight. But does the ability to lift a heavy weight enable one to call themselves a strongman?......... I think not.
In my opinion, to be able to call yourself a genuinely strong man or woman. One should not only possess the ability to lift a heavy weight for a single rep but should also possess enduring strength. The ability to miss a nights rest or meal without showing any ill effect. The ability work if necessary morning, noon and night with unflagging energy and a clear mind.
I wouldn't consider a person of great physical strength but mental frailty to be truly strong just as I wouldn't consider a person strong if they developed their body out of proportion possessing a strong chest and arms but comparatively weak legs and back.
This is not to disregard the ability to display maximum monetary strength as I have devoted many countless hours to developing this kind of strength and believe that the key to developing many areas of mental toughness can be formed in the pursuit of strength. To become truly strong you must be able to endure mundane periods of training, setbacks, plateau's all with an unwavering focus and unrelenting energy, to do this is no small feat and will require a high level of mental fortitude.
Just as a physically weak man can make himself strong with careful and patient training, so can a man of weak thoughts can make them strong by exercising himself in the right thinking. Just as a gardener cultivates his plot, keeping it free from weeds so may a man tend the garden of his mind weeding out weak thoughts.
"They themselves are the makers of themselves by virtue of the thoughts which they choose and encourage" James Allen
To be called truly strong, then a person must focus on developing all areas of their constitution, which encompasses the body and mind completely. Developing mental grit is equally if not more important in the long term. As it is this Grit that enables you to push through the tough times, to pick yourself back up after set backs and keep moving forward. And as we all know that consistency plays a major factor in strength development.