If you're in charge of your website and how it appears on the search engines, you've definitely heard of Google's "Panda" and "Penguin" updates.
No? Well, simply, they were major changes to the algorithm Google uses to decide which sites rank well (and which ones don't). Meaningless, spammy links to your website were no longer given credit -- in fact, Google penalised sites it thought were using slimy methods to "game" their algorithm. Have a look at this page on my main website for more info.
Some sites saw their positions on Google go through the floor (which, of course, directly affected how many potential customers were finding them). Some sites actually did better than before.
Do you have any idea how your site did? No? Interested in finding out?
All you need to find out is a current Google Analytics account that is able to go back a couple of years. If you haven't yet set up an account or have only done so recently, this won't, I'm afraid, work for you.
Then go to Barracuda Digital's "Panguin" tool. It'll show you the dates of the major updates and how your site's traffic was affected in a very easy-to-follow graph. You'll no longer have any doubt about whether your site was affected by the updates.
It was a... sobering* experience for me.
*I'm using the word "sobering" in its less conventional "Heartbreaking, promoting suicidal feelings" definition.