1) It starts to rain or gets windy and a client was not wearing appropriate clothes and gets very cold in a potentially dangerous situation. 2) A client has worn something extremely uncomfortable and chafes or does not have the freedom of motion to move around properly which ruins the day or slows it down. 3) The client damages their nice clothing and is annoyed.
Enforcing proper clothes for an outdoors trip is a cover-your-ass technique which is necessary when you have been guiding for long enough. I have sent people home because they have not followed the instructions and brought appropriate clothing.
Sure it's just a metaphor but it's extremely triggering for anyone who has been in the guide's situation and makes poor basis for an article on building.