It can be really hard to attract traffic to a website. The competition is though and almost everyone know basic SEO. Conclusion is that you need to get as much as possible out of each visit. In web traffic/analytics language this is called bounce rate – the number of page views per visit. The higher the number the worse your situation is. It is hard to generalize and say what a good enough bounce rate is, but if you can keep it below 40-50% you’re doing OK. I’m not saying that navigation can fix your bounce rate alone and there are many other thing you can work with. However good and user friendly navigation may help users find what they are looking for if the entry page they landed on is not the right one. It may also invite them and create curiosity to go deeper into the site and just look around.