This is an proverb which is easy to affirm when the weather is calm; much harder to affirm during the storm. That being said, it is the storms that shape us and form us into the leaders we become.
I read alot of book on leadership and one thing I have found common in all great leaders; they have all gone through a crucible of some kind, and come out the other side better for it. These crucibles tend to come in three forms; test, trials, and tragedies. Depending on how you face them and how you endure them, they can either crush you and send you spiraling, or they can be a catalyst for growth.
Crucible: a severe test.
Catalyst: an agent that provokes or speeds significant change or action.
When faced with a crucible, some sort of test, trial or tragedy, how do you tend to react? It reminds me of something Winston Churchill once said,
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
Do you aspire to be a leader, to be great? Do you hope for influence and a position of authority? Do you desire to to fully utilize all the gifts and potential that is within you? If so, you must prepare yourself to face the "fires" of life which are needed and necessary to refine you into the great person that God has created you to be.
I remember my HS Basketball coach who, after one particular hard practice pulled me aside and in love reminded me, "Mike - don't be worried when I yell at you or correct you. It's only because I see the potential in you. It's when I stop yelling at you that you should be worried." In a similar way, God allows us to face these crucibles in order that we might be more fully used by him. Reminds me of yet another saying;
"...being confident of this, that he who began a good work in you will carry it on to completion until the day of Christ Jesus." (Philippians 1:6)
Remember - the stronger the storm, the stronger the trees.