White seems okay here but is in fact lost! However only an engine could see and play the brilliant knight sac.
[d] 2b2rk1/1pp2pp1/2n2n1p/8/1P4P1/1Q1PP2P/r3BK1N/qN1R3R b
1... Nc6-d4 2. e3xd4 Qa1xd4+ 3. Kf2-e1 Bc8-e6 4. Qb3-c3 Qd4-f4 5. Rd1-d2 Nf6-d5 6. Qc3-c5 Ra2xd2 7. Nb1xd2 Rf8-a8 0 - 1
[d] r5k1/1pp2pp1/4b2p/2Qn4/1P3qP1/3P3P/3NB2N/4K2R w
Here white is lost despite still being a piece up.
Do you honestly think that Kasparov or Fischer could have seen it too?
Now cracks a noble heart.—Good night, sweet Princess, And flights of angels sing thee to thy rest!
[d] 2b2rk1/1pp2pp1/2n2n1p/8/1P4P1/1Q1PP2P/r3BK1N/qN1R3R b
I would just play Rb2 here instead which wins the pawn on b4 and gives black an advantage (although white can still probably draw this) and so clearly not as cool as playing Nd4! which just wins.
Now cracks a noble heart.—Good night, sweet Princess, And flights of angels sing thee to thy rest!
Jack Lad wrote:White seems okay here but is in fact lost! However only an engine could see and play the brilliant knight sac.
Yes this is one small reason why humans lose from engines, but i think the main reason is the mistakes they make:
For example in the Anand-Gelfand world championship 2007 game, black in the following position played Rxe1? and offered a draw. Anand accepted. Every engine can find on the spot the Rxf4 which is immune from the Queen because of Bg5.
[D]3q2k1/ppp2pp1/3p1b1p/1b5P/4rPN1/1PP5/P1PQ1BP1/2K1R3 b - - 0 22
After his son's birth they've asked him:
"Is it a boy or girl?"
YES! He replied.....
However only an engine could see and play the brilliant knight sac. 
Yes indeed humans are very prone to making silly errors and oversights whereas engines rarely make such obvious blunders.