You know that little tag on your keychain for your local supermarket? The one where they have your name and address on file, associated with the barcode on that keytag? The one where you can't get anything on sale at the sale price unless you give the cashier the tag to scan? The one where they know all your buying habits at their store?
They know everything you buy, how much, how often, what time of the day you like to shop, what day of the week you like to shop.
And if you buy too many plastic sandwich bags too often, the cops may show up at your door with a search warrant, to look for drugs. (it has happened to people already)
And we don't only have a bunch of Big Brothers watching us, we got a ton of Little Brothers too.
What about the average person on the street with a camera in their mobile phone? Are they snapping pics of you, uploading them to social networks, and making remarks about you? I have seen profiles of guys that do this, snapping pics of women they see on the street, uploading them and tagging them with rather rude/crude captions. And then those pics get indexed by Google and a bunch of other search engines. Then there is the bunch of people that use Google image search to find pics for their blog posts, web sites, school projects, etc. How many people could potentially end up with that pic, using your likeness in ways you would never approve of, and you don't even know the image exists?
In this modern day and age, privacy is an illusion. The only real privacy you have is in your mind (and only as long as you keep your thoughts in there and don't let them out)