In Spassky v Fischer '72 game 11, why is 14. Nb1 considered such a great move? In game 11 of the 1972 World Championship, Spassky as white moves his Knight back to its 14. Nb1 starting position. Apparently, this moved was received as 14. Nb1!!. But to me, it seems as a simple attack on the invading black queen to flush her out of the zone.

What about this move makes it so interesting?

Shown below is after move 13. Kh1 Bd7

[FEN "r3kb1r/1p1b1p2/p1nppp1p/8/4PP2/qNN5/P1PQB1PP/R4R1K w - - 0 1"]
Taking a look at the comments in your link, I came across a post quoting GM Edmar Mednis:


  A move which was invariably given two exclamation marks - 14.Nb1!!
  after the game. May I respectfully suggest that if Spassky had
  proceeded to lose this game it would have read 14.Nb1?? If we look at
  the nature of the position, it should be apparent that neither of
  these extremes is warranted. White has difficulties in how to
  continue, so he decides to first kick Black's Queen. However, this is
  an open position and White's QN is placed well on c3. Retreating it to
  b1 obviously cannot be a winning maneuver. It is simply an interesting
  concept, which works because Fischer has an off game. Under the
  circumstances 14.Nd1!? would also have probably won. As a historical
  note, it may be stated that those commentators who were loudest in
  applauding 14.Nb1!? neither played it themselves nor worried about it
  when their turn came.