Before you'll be able to sell your product or service, people need to trust you.
Before you'll be able to raise money, people need to trust you.
Before you'll get that job, people need to trust you.
Before you'll get anyone to read your book, people need to trust you.
So the bottom line is this:
Build up trust before you need it.
Because if you only start when you really need it, it's usually already way too late...