A recent wobble in Clicks shares — the stock fell as much as 7% on the day it went ex-dividend — has again raised fears that one of the best retail investments of the past 15 years could be stalling.

While Clicks has grown earnings and sales with astounding consistency, its shares are pricey: they trade on a historic p:e of 37 and a forward p:e of 30. That means investors are ponying up a lot of money in the hope that the company delivers on its growth promise...