Sure, not publicly listing every meal you have followed by every bowel movement would be a good start that is never going to happen because the world needs to know this information.
However, that's not the only data that is gathered and sold. The information that is gathered passively from extensive efforts to track individuals across the internet is the elephant in the room that you seemingly want to ignore. These are direct attempts by companies to subvert individuals that might actually NOT be posting every little thing they do on social platforms. Things like tracking people as they move about brick & mortar stores or other types of beacons for whatever purposes they are being used for are examples. SmartTVs gather metrics, grocery stores gather metrics, and the million other "little" things that when gathered together all paint a very very detailed picture about someone without them necessarily knowing about.
so you're "don't be so public on the internet" is not such a simple little thing
However, that's not the only data that is gathered and sold. The information that is gathered passively from extensive efforts to track individuals across the internet is the elephant in the room that you seemingly want to ignore. These are direct attempts by companies to subvert individuals that might actually NOT be posting every little thing they do on social platforms. Things like tracking people as they move about brick & mortar stores or other types of beacons for whatever purposes they are being used for are examples. SmartTVs gather metrics, grocery stores gather metrics, and the million other "little" things that when gathered together all paint a very very detailed picture about someone without them necessarily knowing about.
so you're "don't be so public on the internet" is not such a simple little thing