To overcome an irrational fear...
replace it with a habit.
If you're afraid to write, write a little, every day. Start with an anonymous blog, start with a sentence. Every day, drip, drip, drip, a habit.
If you're afraid to speak up, speak up a little, every day. Not to the board of directors, but to someone. A little bit, every day.
Habits are more powerful than fears.