I'll add my voice to the chorus in saying that a tickler worth his / her weight in salt will switch spots to keep the lee sensitized.
Having said that, there's nothing worse than a tickler who jumps around too much, either. They're missing out on the best parts when they keep attacking one spot after another.
In my opinion, ticklers need to respect the ticklishness curve.
At first, it tickles. For most spots, the first few seconds are more tolerable, because the body needs to adjust to the new stimuli. Plus, the body assumes that this is a quick tickle, and will briefly pass.
After a while, it starts to tickle more. Not only should the tickler be honing in on the most sensitive spots (which they've discovered through careful observation), but the victim starts to realize this isn't going to go away.
Once the reality sets in and the tickler is in a groove, that's when it's really bad. (or is it good?) That's where the begging, the crying for Mommy, the silent laughter, all that comes into play.
Eventually (again, depending on spot), this will begin to fade, and the ticklee is desensitized.
A good tickler will stop just as the ticklishness begins to die down, mere milliseconds after the ticklee is pretty sure the Rapture is upon them. The victim has a few seconds to catch their breath and try to come to their senses, but by that point, the tickler has identified their next target.
