The power grid is often called the biggest machine ever built, and it runs on one unforgiving rule: at every instant, generation must equal demand. There is almost no storage in the wires themselves, so any mismatch is paid for out of the spinning inertia of the generators — and that shows up instantly as a change in frequency.
Sixty hertz (fifty in much of the world) is the real-time scoreboard. Too much generation and the machines speed up, above 60; too little and they slow down, below 60. Drift too far and protective relays trip plants offline to save them — a blackout. Operators watch that number every second of every day.
Sun and wind are intermittent: a passing cloud can drop a solar farm's output in seconds, and you cannot simply turn the sun back up. A gas plant can follow demand, but it ramps slowly, over minutes. A battery responds in milliseconds — it buys the seconds fossil plants can't — but it holds only so much energy before it's spent.
That is why a renewable grid needs storage: not to make more energy, but to move it a few seconds or hours in time so supply can chase demand. Balancing this bench by hand is exactly the job every grid operator does — keeping the needle on sixty.
Something in the simulation stopped unexpectedly — the lesson continues without it. You can move on; nothing you did was wrong.