He also learned, at the ANT, from watching other actors work.
Harry Belafonte was the most prominent of his peers in this period, and the two of them developed a friendship that involved mutual observation and, presumably, mutual learning. Belafonte had different strengths as a performer — a musicality and a physical ease and a charisma that operated somewhat differently from Poitier’s more internal and contained quality. Watching someone with different strengths is one of the best ways to understand your own, to see what you’re reaching for that they seem to have naturally, and to see what you seem to have that they’re working toward.
The formal instruction at the ANT was supplemented by the janitor work, which was its own kind of education. Poitier mopped floors and cleaned toilets and cleared the stage and set up the chairs for rehearsal. He was in the building constantly. He saw everything. He watched rehearsals from the wings and from the back of the house. He saw actors making choices, directors responding to choices, scripts being rewritten in the room. He saw the machinery of theatrical production in operation from the inside, from below the level that would normally be visible to a performer.
This kind of institutional knowledge — understanding how the whole apparatus works, not just your piece of it — is not typically part of formal actor training. You learn it, if you learn it, by being present over time in a working institution. Poitier’s apprenticeship gave him that.
By the time the accident of Belafonte’s absence and a Broadway casting director’s presence gave him his first Broadway opportunity, Poitier had been preparing for it for months, through every modality available to him: the private study, the reading lessons, the radio, the janitor work, the watching from the wings. The opportunity looked like luck. It was luck, in the specific sense that no one had planned it. But the ability to take advantage of it was entirely the product of everything he had built.