For example, we will consider the design of a large airliner, one which is slightly bigger and faster and can go further in greater comfort, and cheaper, than the best of today's airliners. As we write out the mission profile, various other requirements occur to us. The aircraft must be able to take off from any large city airport, in hot weather. And be able to take off, no problem, even if one engine quits just as the aircraft is lifting off the runway. And land safely even if one engine quits when the aircraft is as far as it can be from any airport.
Aerospace engineers think about everything that can possibly go wrong, and many things beyond that.
And then they worry, and plan, and check their calculations, and talk to other people about how to improve their estimates and calculation procedures. They develop simulators to test out every eventuality. Nothing is left to chance. Structure Strength of each part, material, weight reduction, life prediction. Break this down into steps involved in manufacturing.