Build it and they will come?

First, the "build it and they will come" mentality is a fallacy. You need to build something great and have distribution in order to succeed. And distribution is hard to get.

There are many ways to get distribution. One of those is through press. If you have a great product, the more people that find out about you, the more people will know about you. And they'll tell their friends, who'll tell their friends, etc.

Another subtle press benefit: you're getting links from a bunch of very highly-regarded sites, and this helps out your rankings in search engines quite a bit, which builds more traffic.

There are plenty of other good ways to get traffic too, such as engineering for viral growth, but press can have huge benefits for the right product.

Second, in order to get people to use your product, you have to stay alive. This sounds obvious, but a ton of people spend 6 months building a product, launch it, and give up within 3 weeks.

Plain and simple, it's going to take time for people to start using your product — there are exceptions, but it's generally not the norm. So you need to expect that, and be willing to give it time. If you give up within a month or two, your product definitely won't be successful.

Once you launch, people start to know about you. If you launch early, you can start earlier on the process of acquiring users. Don't launch with a crappy product — launch as soon as what you have is better than what is out there. But don't wait for a perfect product — launch as early as you can, get user feedback, and keep improving the product.