How would you feel if you were looking for ‘pizza shops in Dallas’ and reached a site with a tutorial to make a strange named mock-tail with the keyword ‘pizza shops in dallas’ thrown here and there? Of course you won’t react in a positive way as you didn’t get what you want and you’ll have to start the search over again from the beginning; unless, well if you were looking for a mock-tail to go with your Pizza!
Google also (claims to) understands it and is constantly trying to provide users with good results which the users are actually interested in and not some over optimized irrelevant site. It however has to rely on a pre-written algorithm to do the search for you and bring back the most relevant results with greater emphasis to results which may be best suited for you. However even though the same was never disclosed by Google, people did manage to get an idea of the algorithm and tried to manipulate their websites (Website optimization) accordingly so that they will get that #1 spot when someone searches the keyword.