When search engines crawl your site, there are certain words they are programmed to ignore - these are called "stop words" - and include words like:

I, a, about, an, are, as, at, be, by, for, from, how, in, is, it, of, on, or, that, the, this, to, was, what, when, where, who, will, with, the...

This means that in order to save space, the search engines don't actually index these words in their database. Furthermore, when you're actually searching using these terms, they are also ignored. This can be quite irritating - BUT fortunately, some search engines let you use a "+" operator to force them to include the stop words.

For example

"a life less ordinary" returns #1 hit as a movie on the IMDB website
"a life less ordinary -movie" returns #1 hit as some sax music from the Amazon website
"+a life less ordinary -movie" returns #1 hit as a book on The Hindu website

Just to confuse the issue, "stop words" has an entirely different meaning in Adsense. In Adsense it refers to a list of words which may prevent normal Adsense ads displaying and instead show public service ads. These words include things like profanity, drugs, death and disaster...