The first couple of weeks I learned JCL and the IBM mainframe. There were two old guys who worked there, my age today I imagine, and they worked on 6 batch applications simultaneously, making a single compile/run cycle per day for each.
Even today I can’t imagine how. We thought of them as a pair of Yodas (of course not the real Yoda, he didn’t exist yet).
They starting programming when computers were coded with wires.