notyetagm: <IMlday: Missing 19. Ne4 could happen to anyone.>
Yes, the <LOOSENESS> of the d7-square right next to the Black e8-king is fatal.
It really is amazing that in spite of the fact that the Black pieces surround the Black king, Black has so little control over the critical light squares d7 and f7 next to his king. The Black pieces cover c7 three times, e7 three times, and g7 twice, but only the Black king covers d7 and f7!
One of the most glaring tactical weaknesses is a <LOOSE SQUARE NEXT TO THE ENEMY KING THAT CAN BE COORDINATED ON>. Here the White b7-rook makes the Black d7-bishop/d7-square loose. The White d3-queen is all lined up and ready to play ♕x♗d7+ and ♕xf7#. The only Black piece meeting this threat is the Black d5-pawn, by <BLOCKING> the d-file from the White d3-queen to the d7-checking focal point. Unfortunately for Timman, since <BLOCKING A LINE IS A FULL-TIME JOB>, the Black d5-pawn cannot also <DEFEND> the e4-square to keep the White c3-knight out and White wins immediately with the bone-crunching 19 ♘e4!.
The defensive power of a pinned piece is merely illusory, aka, <BLOCKING A LINE IS A FULL-TIME JOB>. The Black d5-pawn, <PINNED> to the d-file to meet the threat of ♕d3x♗d7+ by <BLOCKING> this line, only -pretends- to <DEFEND> the e4-square.