Cookies are annoyingly broken.
Particularly when you're going about your business and up pop supposedly targeted Google ads from competitors. And all because genius marketeers inside competitors make Google ad assumptions which conclude that people who visit websites of their competitors are likely to be thinking about buying new accounting software for example, so let's be ultra targeted and serve them ads for our alternative.
And so, because I visit xero.com as a user and an employee, the cookie tracking cruft that builds up in my browser cache tells ad servers that I ought to see adverts for competitors of Xero.
Even if I'm watching something entirely contextually inappropriate.