Squashing a solid flat throws away its depth — and that's exactly where things go wrong. Two solids that are very different behind the front can flatten into the same front view.
Hidden Edges, Drawn Dashed
When you draw a solid, some of its real edges sit behind the parts you can see. You can't see them, but they're really there — so they get drawn as dashed lines instead of solid ones. In the toy, toggle the hidden edges on and off: the dashed lines are the back corners of each solid, tucked out of sight. A solid line means "edge you can see"; a dashed line means "edge that's there but hidden".
The Proof That One View Isn't Enough
Press "surprise me". You'll see two solids that look identical from the front — both give the same L-shaped front view — yet they're genuinely different objects. One is a thin L slab; the other is twice as deep. The front view alone can't tell them apart, because flattening from the front hid all that depth. That's why a single drawing is never a safe description of a solid.
So Always Use More Than One View
To pin a solid down for certain, you need the front, the side and the top. The side view is what would expose the difference between those two L-solids — one would look thin, the other deep. Three views together leave no room for two different solids to sneak through. When a question gives you only one view and asks "what's the solid?", the honest answer is often "it could be several things" — and that's the insight this rung is really about.