This means you need lines that will let you fish from the surface, down to the bottom. Sure, you might get by with only one line and catch plenty of fish if conditions are just right. But this is rarely the case. More importantly, I take the time to change lines if the conditions so warrant. Too many anglers don't bother with this, and will continue to fish over the same water, with the same techniques, long after the fish have turned off, or have switched their feeding preferences.
Anglers often mistake slow periods as non-feeding times.
It is imperative to keep this in mind. I feel that not nearly enough attention is paid to tippet size. More often than not, I have found the solution to refusals to be nothing more than downsizing the tippet diameter. I have never felt this to be a necessity myself. Recently a new tippet material came on the scene.