"(There's) no such thing as a stupid question" is a common phrase, that states that the quest for knowledge includes failure, and that just because one person may know less than others, they should not be afraid to ask rather than pretend they already know.
[1] A 1970 Dear Abby column in The Milwaukee Sentinel said: "There is no such thing as a stupid question if it's sincere.
[3] Presentation Skills That Will Take You to the Top says that within the business world, the adage holds true.
"[9] Breaking into the Game Industry argues that the adage (and the related one "the only stupid question is the one that is never asked") is only relevant for the classroom and that in the real world when you want to try to impress someone, there are many stupid questions one can ask.
[10] School House Diary: Reflections of a Retired Educator notes that teachers are fond of saying this phrase, and suggests that while they themselves want to call out the stupid questions, they fall back on the adage in order to prevent the child from being ridiculed.