That's what happened in this game. Barda saw Keres' threat and calculated five moves ahead and thought his 20.Kf2 left him with a won position. But, the sequence wasn't over and Keres saw a couple of moves further...to the real end of the sequence.
Paul Keres needs no introduction. He was an aggressive and a swashbuckling player and this trait never left him even though in his later years his play was a little more positional. That's because as a player gets older it gets harder to calculate tactics and so one tends to rely on experience and intuition more.
His opponent, Olaf Barda (August 17, 1909 – May 2, 1971), born Olaf M. Olsen, was a Norwegian who was the first Norwegian player to be awarded the IM title, which he received in 1952. Barda won the Norwegian Championship six times: 1930 (under the name Olsen), 1947, 1948, 1952, 1953, and 1957. Barda was also a strong correspondence player, winning the Norwegian correspondence championships in 1946 and 1949/1950. In 1953 he was awarded the correspondence GM title and finished fourth in the First World Correspondence Championship played between 1950 and 1953.
This game was played in the 12th Chess Olympiad which was held between August 31 and September 25, 1956, in Moscow. The Russians were were double defending champions and lived up to expectations although their margin of victory wasn't as big as in previous years. Yugoslavia and Hungary finished second and third.