Try, try again -- but how quickly?

[lefty]

In the "Flounder Tips" thread, hampsteadfishing recommended trying certain lure combinations and then trying something else. I'd like to ask the stupid novice question of the day -- how long do you try before trying something else?

I guess I've got a fundamental confidence problem here -- how do I know whether I'm doing something wrong (retrieving too fast, too slow), or I'm using the wrong bait or the wrong lure, or I'm just in the wrong place? Or whether they just ain't biting?

Some of this comes from my engineering background. I'm trying to isolate the variables, and it ain't working in the least...

Lefty