You’re probably aware of what Starbucks did recently at all of its 7,100 locations throughout the U.S. But you may not know why they did it. You should.

“America’s favorite drug dealer“ (not my line, but from the Starbucks Gossip blog) closed all of its stores for 3+ hours, throwing thousands into panicked latte withdrawal during the critical 5:30 to 9 p.m. time slot. The reason, it was reported, was to re-focus its attention back to making coffee. Training sessions were conducted to ensure that barristas were doing their job – crafting espressos and other unhealthy libations – with the quality and efficiency that helped make the company so extraordinarily successful.

Yes, I know what you’re saying – “They’re making coffee, for crying out loud!“ – but Starbucks has wandered off into other areas in recent years, from music and book distribution to breakfast foods. Perhaps it was not so coincidental that the company got hammered on its P&Ls in 2007, and its economic woes forced a restructuring of the company that included layoffs of more than 600 employees.

Call it a PR stunt, but Tuesday’s move by Starbucks is an example of why companies should never lose sight of what made them successful in the first place. Those of us who dabble in marketing casually throw around phrases like “core competencies“ and “skill sets.“ The point is, you do what you do best, and you keep doing it. Extending your brand is all well and good as long as you can keep your loyal customers from bolting to Dunkin Donuts for their Caramel Frappaccino fix.