It is not surprising that Google seems to know what everyone is doing. They get input through:-
Their search engine (Google Search)
services designed for work and productivity (Google Docs, Sheets, and Slides),
email (Gmail/Inbox),
scheduling and time management (Google Calendar),
cloud storage (Google Drive),
social networking (Google+),
instant messaging and video chat (Google Allo/Duo/Hangouts),
language translation (Google Translate),
mapping and turn-by-turn navigation (Google Maps/Waze/Earth/Street View),
video sharing (YouTube),
note-taking (Google Keep),
and photo organizing and editing (Google Photos).
The company leads the development of the Android mobile operating system, the Google Chrome web browser, and Chrome OS, a lightweight operating system based on the Chrome browser.
On March 15, 2016, Google announced the introduction of Google Analytics 360 Suite, "a set of integrated data and marketing analytics products, designed specifically for the needs of enterprise-class marketers." Among other things, the suite is designed to help "enterprise class marketers" "see the complete customer journey", generate "useful insights", and "deliver engaging experiences to the right people" Wikipedia, About Google
Ordinary web users like us can edit how our details are stored and used by all these inter-connected utilities, but if we do nothing we continue to be overwhelmed by an avalanch of advertising "tailored to our interests" So it is worth taking a bit of trouble to adjust the settings.