Just to clarify, the fly pictured was not an attempt to trim the hackle to fit the hook. This is a pattern called a thorax-style dry fly. Trimming the hackle allows the fly to ride low in the film and the longer, untrimmed hackles on the sides to act as outriggers to balance and support the fly as well as to give a really good semblance of legs on the surface film. Many patterns are this style and very effective, and I tie and use them often - no taboo if it works.
"There will be days when the fishing is better than one's most optimistic forecast, others when it is far worse. Either is a gain over just staying home."
Roderick Haig-Brown, "Fisherman's Spring"