Here's how it happens:
* Mortimer is initially skeptical of Holmes's abilities. He comes to 221B Baker Street with a case involving a terrifying hound and the Baskerville family curse, but he is not entirely convinced that Holmes can help.
* He dismisses Holmes's work as "unimportant trifles." Mortimer describes his previous cases as involving "small, unimportant trifles" compared to the gravity of the Baskerville mystery. He is focused on the supernatural and the danger, seemingly ignoring the importance of logic and deduction in solving the case.
* He fails to fully understand Holmes's methods. Mortimer doesn't understand Holmes's meticulous approach to observation and deduction, which are crucial to his detective work. He seems to underestimate the importance of mundane details and is more interested in the sensational aspects of the case.
While not directly insulting, Mortimer's actions and words subtly demean Holmes's work, demonstrating a lack of appreciation for his unique skills and methods. This sets the stage for a dynamic between the two characters, where Holmes has to prove himself and earn Mortimer's respect.