I was thinking more along the lines of many people swearing that they have always been able to catch fish during, for example, Caddis activity on CDC & Elk. The next person responds "I've never had any luck with that pattern.

Some, another example, say the Klinkenhamer style fly always produces for them....the next guy says "I've tried those a lot and never catch anything on them.

Another good example are the Gary LaFontaine pupa patterns. Some swear by them....others swear AT them.

Obviously, some of the deviation is due to the presentation, or the frequency of use, but such factors don't seem able to explain such opposite views.