Artists talk about a shape's visual weight — how much it pulls your eye and seems to press on the picture. It isn't real grams. A shape grows heavier as it gets bigger, as it darkens against the page, and as its colour gets warmer.
A composition balances like a scale: weight × distance from the centre on the left must match weight × distance on the right. That's why a tiny dark shape far out can hold a big pale one up close — the frame you see here tips until the two sides agree.
Symmetrical balance mirrors the two halves. Asymmetrical balance trades size for darkness or distance so unlike shapes still even out. Radial balance spreads weight evenly around a centre.
Something in the simulation stopped unexpectedly — the lesson continues without it. Nothing you did was wrong; you can move on.