2. Knowing how the part will be used and how it will age

One of the major constraints is to guarantee the duration of the qualities required of the part. For many constraints, we can refer to real-life measurements, but if the objects we're considering must continue to guarantee a sufficient level of performance over time, we will usually only be able to assess their durability by means of tests carried out after artificial aging or under different climatic conditions. In such cases, we'll need to ensure that we have adequate safety margins.

Example: let's take the case of insulating supports for electrical cables. At the same time, the material must remain insulating over time (at least the time defined by you), and must not deform too much under tightening, at the risk of the cable gradually slipping under less effective tightening. What's more, the material must not be brittle, either initially or after several years...