I’ve touched on this subject here on TT, but it’s never resolved itself this clearly for me.
Being a player is a lot like using a flashlight: You can see things in front of you, and maybe a bit to the sides, very well. On the edges, things are pretty indistinct. Further away (and behind you), you can’t see anything at all.
In other words, what seems clear to you as the GM may not fall under the players’ collective flashlight beam. They might be seeing it indistinctly, at the edge of their cone of light — or it might be behind them, effectively invisible.
When you GM, the key is to put as much fun, important stuff as possible in the flashlight beam. You should also leave some interesting stuff outside the light, in case the players turn in that direction.