The failure modes that show up repeatedly across system designs, how to recognise them before they ship, what a good design actually feels like to work in, and a few habits that compound over a career.
A system survives or fails by how it handles change. Boundaries between components, contracts at the seams, the cost of evolving a live system, and the ownership map that determines who is allowed to change what.
The five things every system design has to make concrete decisions about: data, state, control flow, failure, and observability. Each one is a hinge point where good and bad designs diverge.
How a staff engineer actually approaches a system design in the wild. Framing the problem, separating requirements from constraints from tradeoffs, surfacing hidden assumptions, sketching before deciding, and treating the design as a communication artifact.