Judging by the 5% decline in shares of Under Armour (NYSE:UAA) yesterday, something tells me most investors wouldn't have guessed the performance apparel specialist just reported stellar quarterly results.

Source: Under Armour.

But that's exactly what Under Armour did Thursday in marking its 14th straight quarter of at least 20% top-line growth.

Specifically, quarterly net revenue rose 26% to $723 million, which translated to 27% net income growth to $73 million, or $0.68 per share. For reference, both numbers handily beat analysts' lofty estimates, which called for earnings of $0.66 per share on sales of roughly $710 million.

Better yet, Under Armour once again increased its full-year guidance, and now expects 2013 net revenue of approximately $2.26 billion.

Here's what happened
So why in the world did the stock fall?

Look no further than Under Armour's subsequent earnings conference call, when CFO Brad Dickerson weighed in to say the company expects 2014 net revenue and operating income to be at the lower end of its 20% to 25% long-term growth targets.

What's more, even after yesterday's drop, shares of Under Armour are now trading for 64 times last year's earnings and almost 44 times next year's estimates. Now, I may love and admire Under Armour as a longtime shareholder myself, but even I have to recognize the stock is trading for a premium.

Haven't we been here before?
That said, it's also worth noting Under Armour's habit of underpromising and overdelivering.

In fact, yesterday's results and subsequent market reaction are eerily similar to last year's third-quarter report, after which Under Armour shares fell 6.5% after the company beat expectations and raised its full-year guidance. In addition, during last year's conference call, management used nearly the exact same words to say it expected 2013 revenue to come in at the low end of the 20% to 25% long-term growth rates.

Of course, it also didn't help that in last year's third quarter Under Armour's shoe segment saw a 6% sequential sales decline from the previous quarter, which fostered investors' worries that the small company wasn't effectively competing with industry behemoth Nike (NYSE:NKE). Sure enough, though footwear sales during the most recent quarter did rise 28% over last year to $81 million, they once again decreased from $82 million in the second quarter of this year.

By contrast, Nike last month reported quarterly NIKE Brand footwear sales of $3.979 billion (yes, with a "b"), which represented 2% sequential growth from the previous quarter and 7% growth over the same period last year. And that doesn't even include the 16% year-over-year sales increase Nike achieved last quarter through its Converse brand, which is now being reported in earnings as a separate segment thanks to its relative autonomy to Nike's core business.

As it stands right now, I suppose these concerns surrounding Under Armour may seem fair, so it's hard to blame nervous investors for taking a step back this week.

However, for reference, take a look at what Under Armour stock has done -- even after this week's pullback -- ever since nearly the exact same worries surfaced last year:

UA Total Return Price Chart, NIKE stock

UA Total Return Price data by YCharts.

It's funny, isn't it? While the stock definitely took a hit over the short term last year, long investors who were willing to take advantage of the pullback were ultimately rewarded handsomely for their patience while trouncing the market by nearly 24%.

And that, my fellow Fools, is why I have no intention of letting go of my own Under Armour shares anytime in the near future. Moreover, if Under Armour stock continues to languish over the next few months, I'll look forward to adding to my position soon.