Critical and non-critical functionalities
Engineering protip: Know the difference between critical and non-critical functionalities of your product, e. g. between why your product MUST do and why it SHOULD e.g. for cars engines are critical, stereos are non-critical.
Critical parts of the product should be designed to be simple and durable. Non-critical parts should be cheap and easy to replace and remove. The failure of non-critical stuff should never affect critical stuff.
Critical parts are your “core business”, as business people say — they give you competitive advantage.