This is because most engines & directories place a high level of importance on keywords that are found in your title tag.
The title tag is also what the search engines usually use for the title of your listing in the search results.
The length that the different search engines accept varies, but as long as you keep within this limit you should be ok.
Tag tips: We recommend that you include 1-2 of your most important keyword phrases in the title tag, BUT be careful not to just list keywords.
Unfortunately for some of you there are some site design/set up issues that can make it very difficult for the search engines to list your web pages no matter how well you optimize and submit them.
We list them here, before you get into all the optimization tips, to hopefully save you from trying to list a site that that will be very difficult to get listed.
Since the keywords that you decide to target will be used throughout the optimization process choosing the right keywords is essential.