In life, we find people that naturally has a great fighter spirit, but we also find many others that their courage to fight is diminished by their fears.  Some times in our daily life or at work we all have experienced frustration because we couldn't defend our selves as we wanted and we acted contrary as we had to.
Karate teach us to face our fears with courage and act calmly when we are forced to defend ourselves to avoid to be defeated.
Fears
Are generaly  ideas or feelings that live in the dark of our minds or spirits because we still don't have the courage to bring them to light to face them.  They limit our capacity to act or react in an appropiate maner in the moment when it is necessary. 
But fears can be defeated if we just face them and find the causes of their existence in us.  Karate give us the strenght to face and defeat all our fears trough hard working physically and mentally.
How do we gain on courage?
Karate-do is not  just a selfdefense system.  Karate-do is the way to build us stronger physically and spiritually.  When  a person starts training Karate he or she finds that it demands a strong body to win power and during the training it keeps us focus in our goals.  When training he or she finds his or her weakness and phsysical limits starting an internal fight to defeat their limits and weakness.   The results will be possitive and you will be a better and stronger person.
Courage:  
Is the state of the spirit that enables us to face danger, fear, or vicissitudes with self-control, confidence, and resolution to strugle.