Advertising is inherently hostile and self-sabotaging, in that it competes for your attention with the actual thing you want to see. There’s a huge mental context-switch involved in noticing, comprehending, considering, and then either dismissing or acting upon an ad. You’re being pulled from the material you wanted to read or view, not just visually but cognitively too. The closest analogue is someone shouting at you to distract you from what you’re doing.

Matt Gemmell makes an analogy.

This is, I think, why the “in-Dash” advertising used by places like Twitter and Tumblr makes people so much more passionately mad than banner ads. A banner ad is contextually obvious and thus easily ignored. But scrolling past a “promoted post” on Tumblr throws people for a loop; they’re suddenly left wondering why their friends are reblogging shitty gifs about terrible iPhone games or cell phone plans in between the porn of Captain America getting reamed by the Winter Soldier. A Dash is a curated space–it’s opt-in–and finding someone has invaded it with unwanted content is an emotionally jarring experience.

Ironically, this inability to ignore is exactly why advertisers buy promoted posts in the first place.