Whenever Google displays search results relating to a particular keyword, a high percentage of people would choose to explore the first displayed website. A smaller percentage of people would choose the second one, and so on. Google devides the number of clicks among the search results. This means that the first website or search result will get 42% of clicks. The second gets 12%, the third 8%, the fourth 6%, the fifth 5%, and the sixth gets 4%, and the seventh only gets 3% of clicks. All remaining clicks, are divided between all the other sites listed in Google.
What this means is, that even if you are the number one ranked website in Google for a particular keyword - there are a lot of people who search with that particular keyword - the number of people who actually click-through to your website, creating traffic, does not necessarily have to be equally high. So if you are optimising your website do not get too excited when particular keywords get high search results. Sure, they are part of your optimising proces, but they do not automatically lead to traffic increase.