This is an example of binary thinking prevalent in self-help books. The scientific reason is, IMNSHO, trying to sell books with simple, easy-to-follow logic, which is irresistible when you're in a dilemma. But it is only a good idea when the consequences of the fear are not so great that you cannot quickly recover.

Are you afraid of being homeless and destitute? Good. That is a good fear to have, and you shouldn't "make it happen." Afraid of jumping off a four-story building? Likewise, good. Afraid of bungee-jumping? That one's questionable, but still not a bad fear. Afraid of asking for a date? Okay, you need to do that one a little so you get over it. Short answer? It depends on the fear and the consequences of failure.

I usually do the thing I am afraid of _if my fear seems irrational_. I have had good success with this: about 70% of the time, I overcome the irrational fear, about 30% of the time, I am still just as afraid later. If my fear is healthy, I leave it alone. So far, I have also had good success with this.