I'm not sure how true that is for advertisements. For example, there are many forms of 'hidden' advertisements that are designed to not be seen, and yet influen

I'm not sure how true that is for advertisements. For example, there are many forms of 'hidden' advertisements that are designed to not be seen, and yet influence people. Among them are product placements. Heck, even Hacker News is an advertisement for YCombinator, though it certainly isn't seen that way by many people.