Costco stock is lower Friday after the membership warehouse firm reported a top-line miss in its fiscal fourth quarter, but Wall Street remains bullish.

If sales and profits grow faster than Costco stock, its valuation, which is at record-high levels, could finally come down to earth. But instead, a frenzy of bull-market enthusiasts who will come out of the woodwork if interest rates are cut could keep it elevated. If that happens, it's likely to drop at some point.