It's a nice moment and all but I don't know if blaming the customer is really the big problem here. Most guys I know aren't sitting around mad at homeowners, they just don't want to crawl under a house for the third time because the last guy taped a pan to a joist and called it done. The fungus is gonna fungus no matter whose feelings are involved. Feels like the old timer said a wise sounding thing and everybody nods along because it sounds deep. Sometimes stuff just breaks or grows where it grows and nobody's really at fault.
That line about quitting blaming the customer for fungus really hits. I've been there, catching myself getting mad at people for stuff they didn't even know was happening under their floors. The old timers always seem to know when to say the one thing that sticks with you. It's a good reminder that most of the time the customer isn't the problem, we just want them to be so we don't have to look at our own work. Bet that one's gonna stay in your head for a while.