The skills and knowledge required to make a well-crafted artefact take a long time to learn. They are the result of repeated practice.
This leads to expertise, or mastery of the craft, and good judgement.
The maker also has intimate knowledge of the materials used.
Much of this knowledge will be tacit: it cannot be written down or easily shared with others.
In the case of mass manufactured artefacts the skill is focused early in the process. The tools, machinery, and process used to make each artefact must be well-crafted.