In the position below Minic just had to play one move to reach the time control and, in those days, the adjournment which would have given his team a chance to find the win. Unfortunately he blundered with Bd5 and the win was gone and the game was agreed drawn without resuming.
[fen ""] [Title "Bellon - Minic, Siegen Olympiad 1970"] [Startply "79"] 1.e4 c5 2.Nf3 d6 3.d4 cxd4 4.Nxd4 Nf6 5.Nc3 a6 6.Bc4 e6 7.Bb3 b5 8.O-O Be7 9.f4 O-O 10.a3 Bb7 11.Qf3 Nbd7 12.Re1 Rc8 13.g4 Rxc3 14.bxc3 Nc5 15.g5 Nfxe4 16.Qh5 Qc8 17.Re3 g6 18.Qh3 e5 19.Qxc8 Rxc8 20.fxe5 dxe5 21.Nf3 Nxb3 22.cxb3 Bc5 23.Nxe5 Nxg5 24.Kf1 Bxe3 25.Bxe3 Ne6 26.c4 f6 27.Nd7 f5 28.c5 f4 29.Bf2 Rd8 30.Rd1 Bc6 31.Nf6+ Kf7 32.Rxd8 Nxd8 33.Nxh7 Ne6 34.h4 Kg7 35.Ng5 Nxg5 36.hxg5 Kf7 37.Bd4 Ke6 38.b4 Kd5 39.Bf6 Ke4 40.Kf2 Bd5 1/2-1/2
I could ask how does black win from the position after white's 40th move but you would all just plug the position into your engines. So, instead:
Why was Bd5 a blunder? How did it give his opponent a chance to save the draw.
Hint: This question is based on analysis by Artur Jusupov in a Chess24 video a few years ago. Freedom of movement is more important than material.