Search then visit a site, google knows.
Visit a site by address and that site uses google stats, google knows.
Visit a site by address and that site has google Ads, google knows.
Visit a site with no google Ads or stats but go via, or later to, one that does, and google knows of both.
Make one accidental search when signed into google and all of this information is linked to your IP and name. OK you think, I use a fake name on-line, but in no time you supply your real name to a bank or place needing ID, say your ISP. In no time at all your name, IP and history are linked. Go to an internet cafe, leave a short history, log into mail briefly, that history is linked to your profile too. Get a new PC in a new home and in one move your histories link up again.
They profile you. This is a powerful tool for them, they don't much care that you are Bob Smith and search for Zen, the meaning of life and scented shampoo and they don't follow each individual history so paranoia can be put aside there. What they do though is to profile humanity and if they were asked to, they could easily provide that profile to an agency you don't want involved in your life.
Are your heath, wealth, interests, hobbies, address, bank, places you visit (on-line and the ones you use their map tool to find) theirs to use for marketing and more or are they your business alone?
Use Duck Duck Go or a similar private search engine.
Depersonalize your web presence with new ID's. Note though that if you delete your google history, even all of your gmails, they still have them. You're just deleting them from your view and they don't delete anything, ever, it's all too valuable to them.