Partly because they’ll know which ones they see least and/or have an easiest time with, but also that the perfect unbreakable machine doesn’t exist; accidents & “acts of god” (as in the insurance term) happen even to the best built appliances. E.g. there’re not many control boards that will survive a lightning strike.
Finally they will know other repair people and will talk shop with them from time to time, not least of all because they also need to buy appliances, and they know this same rule.
Partly because they’ll know which ones they see least and/or have an easiest time with, but also that the perfect unbreakable machine doesn’t exist; accidents & “acts of god” (as in the insurance term) happen even to the best built appliances. E.g. there’re not many control boards that will survive a lightning strike.
Finally they will know other repair people and will talk shop with them from time to time, not least of all because they also need to buy appliances, and they know this same rule.