Optimism is the faith that leads to achievement. – Helen Keller
An interesting thought; however, as Christians we are encouraged to turn it around a bit. We grow and nurture our faith which gives us the optimism that we can achieve anything with God. Take your faith (and God) into everything you do and you'll achieve greatness. Optimism is simply God showing us our way.
And we know that in all things God works for the good of those who love Him, who have been called according to His purpose.