There are two vital and related concepts to keep in the forefront of your mind, your data and your communications.
Your data are bits of information you have, such as an account number, or information about you, such as what you ate for breakfast.
Your communications include things like your phone calls, what you viewed on the Internet, and what you say in public places.
They are related. For example there is data about your phone call, such as when it occurred, the numbers, locations, and possibly who was on the call, the voice recording of the call and the transcription of the call. All these pieces of data are collected for the most trivial call and stored permanently no matter who you are.
These little bits of information about you can then be collated into what is called big data. A growing number of techniques are then used to examine these minute details about you to know you, and control you in subtle or overt ways.
There is a good example from history of what can be done with these little pieces of information we leave in letters, emails, and phone conversations. Consider how often you quote something, some news you heard, a line from a movie or book, or the Bible. Using essentially big data techniques on the collection of personal documents from the first few centuries, you can virtually rebuild the entire New Testament from quoted passages in alone. Piecing together the data about you forms a bible about you that the holder can use to know you and control you.
Consider how this control is done. If you are with a group of friends and are discussing a song, book, or movie, and all but you have fairly unified feeling about the subject, you might be willing to occasionally have a somewhat different view. If it is your norm you will build a reputation. If this is coworkers it might be more uncomfortable to be out of the norm. If is a boss, you might be all the more unwilling to be outspoken. This should give you a hint of some of the ways you can be influenced or controlled.
Consider the idea amplified a bit. You are part of a group that collectively does something unethical, immoral, or illegal. Perhaps it is a minor issue, or it might be a major issue. Collectively you all know you are involved. Collectively there is a lot to lose or a price to pay. How free are you to expose what has occurred or is occurring?
Perhaps it is the collective waste of time that is billed to a third party. Perhaps lies are told to enhance stature or profit. Perhaps is it harm caused to others for collective gain. If you are a part, if you have received gain, you are now controlled, you are no longer free.
When the collective is a large institution, such as government, corporate, religious, or fraternal, the control wielded is immense. The violation of the institutional mandate can be costly. It might be just reputation or funds. It can get as severe as prison, torture, or death. At this point, privacy matters. If you have given up your privacy on the trivial, don’t be surprised when the costs grow.