There are various myths about traffic on the Web, most of which are down to wishful thinking.
Build it, and they will come
No, they won't. There are literally billions of pages on the Web, and you need to promote yours.
If you make a very good site that people find useful (this particularly applies to hobby sites) then it is possible to gradually build traffic without spending anything; the people who came to your site tell their friends, make links to it, and your site gradually gets more popular.
You will still need to get the word out initially, for example being part of the appropriate online communities and letting them know.
In order to get traffic this way, your site has to be top quality, and you have to keep it updated so that it becomes better and better.
Search engine results are what's important
Even if your site ranks highly on a search engine, that won't do you much good if the keywords are rarely typed, or if the people typing those keywords aren't likely to actually be interested in your site.
As indicated before, search engine results are less helpful for local (non-international) sites.
Promotion via the Internet is cheap
Although you can create a Web site without very much cost, actually getting people to go there is likely to require spending money.
Traffic is the be-all and end-all
If a small jewellery store receives 200 visitors in a week, and one of them is interested in placing an order, that's a better result than receiving 2,000 visitors, none of whom actually buy anything.
In fact, if your site gets sufficient traffic, you will find yourself having to pay more for Web hosting because of the bandwidth used by sending out all the files - this can be a particular problem if you offer large files like music or video clips.