This is the first time that I've ever heard someone mention only catching fish while trolling one way. Very interesting.
Maybe it's because fish are holding on one side of something (structure, etc) for some reason (current, sunlight, anything really), and whenever rigs are pulled in the magic direction, it's pulled past the fish in such a way that they're able to pounce on the lure, rather than not seeing it coming or vice versa...?
I'm not sure, but it's still interesting..........