There are many types of strength and things that can be perceived as it, but in many occasions some manifestations of strength are actually product of a circumstantial reaction from fear to life itself.
True strength only comes when a person knows himself achieving a degree of autonomy no many look for. When someone looks for living as human being in all the extent of the word; no depending on another, or exploting others, nor expecting anything from anyone.
One has to work to reach a point through conscious work in which one can discover their own virtues and limitations, in a completely honest way, without filters or mind tricks, fully aware of their finitude, without fear of death or pain.
See the whole history of your life and see how you reached the point you are now, for good or for bad, the whole history of what has given result to what it is now. Your wishes, your fears, and all that makes us humans.
Many times we encounter ourselves falling into the same patterns over and over, letting ourselves be carried away by anguish, irrationality and a spiral of things that formed those same patters.
The only way to avoid this is being a more self aware person, to be able to sort out any situation and become stronger. The true strength comes from the inside is not just the way we react but the state in which we are, and how easily can that state be altered by external factors. Any experience can be a growth and learning experience.