Do We Have This One?
"Just think of all the trouble we could have saved
if we just threw fruit at him in the first place!"
- Ernie, from Mousehunt
, referring to a mouse he and his brother previously attacked more elaborately, but managed to knock out with a piece of fruit he actually meant to throw at his brother but missed.
So an individual or a group is trying all kinds of expensive, or complex, or otherwise troublesome means of doing something because they do not expect a simpler approach to be effective. However, often by accident, a simpler approach is revealed to be more effective after all. Cue a character talking about the trouble they could have saved.
Note that this is not Why Don't You Just Shoot Him?
. That trope could apply for elaborate schemes designed just because Evil Is Stylish
and they do not want to settle for something simple. This is specifically about when one relies on troublesome means because one assumes that they would be more effective.