Curate, connect, and discover
Danny doesn't have the best spatial awareness, you'd think he would given his bout as a vigilante, but his rogues all had the convenient ability of setting off his ghost sense and letting him know when to turn on his awareness.
So when he was taken in by Bruce Wayne in Gotham, far away from any ghosts or portals, he just didn't have any reason to be on guard. It worked well for him since his vigilante days were over and he could put all his focus on school again.
But you see, when he was first taken in, it was just him and his foster brother Tim staying at the manor.
Fast forward to now, Danny gets home from school to find not only Bruce waiting at the table for dinner, but a kid who looks surprisingly like Bruce??? The kid is small, rude and trying to be threatening in a way Danny doesn't really see as such, like the kid is like 8 how much could they really do???
Turns out a lot.
After Danny and Tim sat down and the introductions were made, Bruce filled them in on the situation that was Damian. Tim seemed to take it as a new puzzle, looking to Damian and Bruce periodically as if he could get answers simply by staring. Danny took it in stride, it isn't that unusually for a rich guy to have secret flings that result in children down the line.
Dinner was in full swing when it happened, there had been some bantering the entire time and many threats of bodily harm coming from Damian which weren't met with as many reprimands as Danny assumed it should. A distinct thunk sound was heard after a particularly harsh threat and Danny looked over to see a knife now embedded in Tim's chair where his head once was.
Before he could react, Bruce was standing with a sharp reprimand and Danny collided harshly with his chair as a new knife embedded itself in his shoulder. He cried out in shock, it has been over a year since his last ghost fight and honestly he forgot how much that hurts!
Aka, Bruce and Dick are forced to take Damian's threats more seriously when the civilian Danny is in the crossfire instead of just the trained vigilante Tim.