On Monday, Apple (NASDAQ:AAPL) announced that it had sold 5 million units of the iPhone 5 over the device's launch weekend. That figure ended up disappointing investors, who were expecting the Mac maker to post sales upwards of 6 million to 8 million units.

Much of the optimism was related to the company's prior announcement that it had garnered up to 2 million pre-orders for the iPhone 5 within the first 24 hours alone. Bulls, myself included, shortsightedly figured that last year, Apple saw iPhone 4S launch weekend sales that were four times its pre-ordered number, so it stood to reason that the company could conceivably achieve another four times multiple, which would imply 8 million unit sales over the weekend.

The problem is that the 2 million pre-order figure wrongly boosted expectations, since the vast majority of those were simply never destined to be delivered on launch weekend. The batch of iPhone 5 units that Apple set aside for launch weekend delivery was exhausted just one hour after pre-orders began on its website. That means only one hour's worth of pre-orders would be included in the launch, while another allotment was reserved for retail distribution.

Of those 24 hours it took to grab 2 million pre-orders, 23 of those hours' worth of buyers wouldn't get their hands on the device for a week after launch, since shipping times almost immediately slipped. It's hard to know how many units we're talking about, unless you have a magic portal into Tim Cook's brain. Piper Jaffray's Gene Munster estimates that we could be talking about a million pre-ordered units -- half of the first 24-hour total -- that will be pushed into October and next fiscal quarter.

Supply constraints are naturally the real culprit here behind the iPhone shortages, specifically the in-cell touch display panels, but that distinct feeling of disappointment that led shares lower upon the announcement can absolutely be tied to lofty expectations that got ahead of investors.