Imagine finding a penny on the sidewalk. Happens all the time right? Now imagine I asked you to go out and find a half-dollar on the sidewalk, but not just any

Imagine finding a penny on the sidewalk. Happens all the time right? Now imagine I asked you to go out and find a half-dollar on the sidewalk, but not just any one, a specific one. But don't worry, you don't have to look everywhere, it's almost certainly in one of the US states on the East Coast. That's the difference here. We don't spend all our time scanning the entire sky down to the dimness level that Planet 9 could be spotted, we simply do not have the resources. Our telescopes give a soda straw view, so we miss a lot of what's going on, most of it in fact. If someone knew already where Planet 9 was in the sky we could point our telescopes there over a few days and confirm it. But we don't, we only know a general area in the sky that it could be, and actually detecting it will require dozens of observations from some of the largest telescopes on Earth. On the other hand, we have detected lots of other objects in the Solar System that would be more difficult than Planet 9 to detect if we had to look for just them, but there are lots of those, and we find them easily by accident as we perform other observations or through surveys. Just as if we decided to go looking for lost change on sidewalks we could find a great many coins, but if we were tasked with finding a specific coin somewhere on the East Coast it would take a tremendous effort (or tremendous luck) to find it.