The bird doesn't have to pick it up, merely kill the deer, start eating & bring pieces back to the nest. Golden eagles regularly kill yearlings. Now admittedly, this deer was a little on the "too big" side, but some animals are really tough or think they are.
did it really think it was going to pick it up.
20 years ago my neighbor's Jack Russell terrier used to play with my Doberman & German Shepherd. There were times that terrier would get pissed off & literally attack either of my dogs. Did he think he could win? Obviously he thought enough of himself that he thought he could.
Same thing with that eagle. He thought he could kill that deer & if you don't think he had the weapons to kill that deer ... check out this photo below.
They just sink those razor sharp talons into the deer's neck & hold on till it's over.