Have you ever realised you were unaware of something you encounter regularly until an external force drew your attention to it? Sometimes I'll watch a show that's been out a while, then suddenly people with avatars from that show pop up everywhere. To some extent that may be algorithms and changes in the content I consume, but for the most part I just hadn't noticed before. Our brains are great at filtering out information that we don't deem relevent – and there's a lot of information out there. No matter how many people have examined the span of the Earth – and I doubt some remote areas have been inspected all that deeply, regardless of our ability to do so – I still think there are fascinating phenomena sitting hidden in plain sight. Nothing is obvious until it's pointed out to us.,(reply>), The official term for this is the "Baader-Meinhoff Effect", incidentally.