Many people worry about their website rankings. Personally I'm more interested in traffic vs rankings but I'm getting off topic. So I'm often contacted by people that are worried because their website rankings have changed. Lately it seems the flux in Google rankings has increased. Here are the results from an oversimplified test to show the flux in Google's search rankings.
Step 1 - Select a unique text string that was not published on any website and returned blank search results.
Step 2 - Place it on some sites so now only these sites filling up the entire search results
Step 3 - Make no changes to the sites and see what happens to the rankings.
Step 4 - Share on WebmasterWorld to demonstrate the concept that rankings can change due to Google and not because of our positive or negative changes even if my example is a bit oversimplified & imperfect. Notice how the different sites which weren't changed moved in the rankings for over two weeks. Apologies to color blind people who might not be able to easily follow the different colored sites