How do you define your threat model? how do you know you've done enough?

I read a lot about knowing your threat model but I find it vague term because if someone is spying on you successfully you won't even know it to start with, for me my "adversaries" are tech giants (apple, google, microsoft and the lot, I always spell their names in lowecase because I don't think they deserve capitals), plus advertisers, I am not really bothered about data about that it needs to be public, (address, electoral records, personal details like …

adversaries advertisers apple don find google microsoft names privacy spying start tech threat threat model