Not true! There are so-called handbook engineering problems -- change the ratios in this gear box -- that can be solved by a monkey with a textbook.
However design-from-scratch hardware engineering usually involves a great deal of iteration. The first phase of designing a new chemical or fluid system is a mini-research project to measure the performance curves of various possibilities under a wide range of conditions, and if none of them are good enough it turns into a blue-sky science project. Radio electronics projects commonly start out as a pile of tiny two-layer circuit boards, one for each subsystem, so they can be cheaply iterated in parallel, instead of having to repeatedly redo a single massive board. ("We have to spin (redo) the system board" not being a happy phrase to a project lead.)
In all the sensor and detector projects I worked on, the embedded real-time firmware was always the bright spot that was practically guaranteed to work.
Don't even get me started about designing research hardware for scientists ...