Why do you expect to understand an expert’s talk, without yourself being knowledgeable about the topic/subject? With all due respect, this cockyness is unfortun

Why do you expect to understand an expert’s talk, without yourself being knowledgeable about the topic/subject? With all due respect, this cockyness is unfortunately quite common with software developers (myself included), as if being good at one thing automatically translates to a different domain. Nobel disease, but even without the Nobel-price?