Right, it's a chain of trust between the layers. The link I choose next to me helps determine the quality of successive links, whether I inspect them or not.

When I buy a wooden shack from a carpenter, I'd never expect them to core-sample every plank to ensure it's good wood. That's because a good carpenter habitually buys wood from a good supplier, and will have the experience to detect other suspicious indicators.

Similarly, my coworker might not have verified the machine code, but I can be pretty confident they didn't vibe-install a compiler by Ken Thompson that puts backdoors into the binary.