"I've got nothing to hide!"
Actually, you do...
Your money, for one. Ever heard of personalised pricing? Anyone who's purchased flights on the internet has seen this. Sites will clock that you're returning to view a flight and will crank up the price.
You've got nothing to show!
When you understand that you are dealing with an entity that is trying to either extract money from you or manipulate your behaviour in some way, it's easier to realise that you should flip the statement: you've got nothing to show.
The 'nothing to hide' thing comes from a clever framing by then CEO of Google, Eric Schmidt. Circa 2006 in an interview he was asked about whether people should be treating Google like their most trusted friend, because they seemed to be doing that. He responded "If you have something that you don’t want anyone to know, maybe you shouldn’t be doing it in the first place." He then goes on to admit that "search engines retain that information for some time". Source Eric Schmidt on privacy (YouTube)
The surveillance business model relies on collective apathy
And the opposite is true: it falters with collective action. If we are all careful to starve the system of our personal data then you hit them in the wallet. If just one person acts, there is no effect on big tech, but if millions do? They need us - we provide their raw material for their machines - so we have power en masse.