For the most part, it doesn't seem that investors are all that happy with Facebook's (NASDAQ:FB) latest earnings release. After tapping fresh all-time highs in the regular session, shares fell as much as 11% in after hours trading. Shares have recovered today, but the drop still represents a clear buying opportunity for investors looking to get into the largest social network on the planet.

Were the figures even that bad?

The figures were good
Total revenue jumped 59% to $3.2 billion. Of that total, $246 million was payments and fees revenue with the remaining $3 billion coming from the core advertising business. At this point, two-thirds of ad revenue is mobile, which translates into $2 billion this quarter. Facebook is up to $6.2 billion in trailing-12-month mobile ad revenue. For a business that practically didn't exist two years ago, that ain't half bad.

All of Facebook's pertinent user metrics also continue to march higher, albeit at a slower pace given how large the social network has become. This isn't like Twitter (NYSE:TWTR), which got crushed following its own earnings report on continued user sluggishness. For Facebook, with a monthly active user base nearly five times as big, deceleration is indicative of relatively high penetration rates.

For instance, Facebook's home market of the U.S. and Canada added just 2 million MAUs this quarter. The geography with the most MAU additions was Asia, adding 16 million MAUs. The U.S. and Canada is Facebook's bread and butter from a monetization standpoint, and the key there is focusing on further growing average revenue per user. In that department, Facebook delivered in spades this quarter, sequentially growing total ARPU in the U.S. and Canada from $6.44 to $7.39.

Over 1.1 billion of Facebook's total MAUs now access the service on a mobile device, representing 83% penetration. In fact, 456 million, or 34% of total users, exclusively use Facebook on a mobile device.

After everything was said and done, Facebook walked away with adjusted net income of $1.15 billion, a 73% jump from last year.

Cost guidance was scary
The real culprit behind the drop was Facebook's guidance, specifically as it relates to the company's cost structure going forward. Total costs this year are expected to jump 45%-50% from 2013, driven primarily by the two sizable acquisitions that Facebook closed this year, Oculus VR and WhatsApp. Since both deals entail considerable amounts of stock, Facebook must recognize hefty stock-based compensation charges.

Additionally, Facebook expects 2015 to be a year of "significant investment" in future growth opportunities. Expenses are expected to rise another 55%-75% from 2014 levels.

It's worth the wait
To be clear, those are some big numbers when we're talking about cost growth, numbers that will inevitably drag on profitability. But at the same time, we're talking about a stock that's priced for growth, trading at 80 times earnings and 21 times sales. For Facebook to ever live up to that valuation, it has to invest in future growth opportunities. You can't have one without the other.

Among other things, video ads are a huge opportunity for Facebook, and pursuing video requires significant infrastructure investments to bolster performance due to the bandwidth requirements. The domestic TV advertising market is estimated at $66 billion, and Facebook wants a piece of it. Mark Zuckerberg noted that Facebook hit a new milestone with videos this quarter, achieving 1 billion video views in a day for the first time ever.

Make no mistake, this is part of the growth process. Tens years from now when investors look back, they'll fondly recall how those investments made in 2015 were totally worth it.

Evan Niu, CFA owns shares of Facebook. The Motley Fool recommends Facebook and Twitter. The Motley Fool owns shares of Facebook and Twitter. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.