The pianist Mischa Hillesum was an abundantly musical and sensitive but also mentally unstable personality. Conservatoire teachers acknowledged his remarkable talents, and audiences were thrilled by his performances. Music was his raison d’être, his defence against dealing with the realities of daily life. He was hospitalised in a mental institution several times during his short life. In 1943, the Hillesum family were sent to the Westerbork transit camp. Mischa died while detained as a forced labourer in the Warsaw Ghetto. Only a couple of his compositions are preserved.

Hillesum was born on 22 September 1920, the youngest of three children of Levi Hillesum and Rebecca (Riva) Hillesum-Bernstein. He was raised in an unconventional, chaotic environment in Deventer, in the province of Overijssel, between Amsterdam and the German border. The family home, with its exotic interior and bohemian atmosphere, was certainly not typically Dutch, and precedence was given to intellectual and cultural matters above all else.

At only three years of age, he amazed everyone with his piano-playing. His small hands raced over the keys, and if he couldn't reach far enough, he used his elbows. Sometimes he sat on the floor, playing with his hands above his head. It was perceived as his way of showing that the piano was an extension of his body, and he charmed everyone with his antics.

By the age of eleven the child prodigy had outgrown Deventer in a musical sense and in the summer of 1932 was sent to a foster home in Amsterdam to pursue his studies at the Conservatoire. The impact of the separation from his parents was somewhat eased by the presence of his elder sister Esther (Etty), who was already living in Amsterdam.

According to George van Renesse (1909–94), a teacher at the Amsterdam Conservatoire, by the age of thirteen Hillesum's ability was beyond the level of the final examination. Perhaps all that remained was to improve on his technique and have some lessons in music theory. There is no trace of him in the Conservatoire archives, and so he may have been a guest student, following customised lessons. He evolved into an extraordinary personality, sometimes perturbing his teachers with his strange behaviour. On one occasion he pretended to conduct a symphony orchestra.