Someone correct me if I'm wrong, but ublock breaks almost nothing because it just allows trackers on pages where blocking it would break something.

So if blocking a doubleclick tracker will stop a video from playing on some page/site, an exception will get added to the block list to just allow it on that page/site.

It makes it 'just work', but imo it's not clear enough in the UI that this is happening and I would guess that most users don't even know.