This commentary previously appeared on Real Money Pro at 8 a.m. ET on Nov 12, 2015. Click here to learn about this dynamic market information service for active traders.

Social media giant Facebook(FB) - Get Report has been a bastion of strength in a relatively weak market. FB's fans cheered strong adjusted numbers from the September quarter while ignoring uninspiring results on generally accepted accounting principles (GAAP).

Whichever way you looked at things, year-over-year revenues grew 41%. Cost and expenses, though, shot up 68% on a GAAP accounting basis, meaning net income only rose 11%. Fully diluted earnings per share, on an expanded share base, only crept higher by 3% under officially recognized standards.

The stock-buying public and most of the analyst community focused on the company's less-traditional accounting. Non-GAAP income was up 42% while fully diluted EPS grew by almost one-third.

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Everybody is entitled to their own opinion of which numbers are more relevant.

Official insiders have made it clear how they feel, though. From last December through August 2015, there were 68 insider sales reported against zero open market buys.

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More recently, a Facebook director decided to cash out about 45% of his holdings, selling more than $96 million of shares just since Oct. 30.

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Why are executives so anxious to exit when the company portrays nothing but great news on the horizon? It appears to be based on valuation. In a year when GAAP earnings may be relatively flat, FB shares are commanding almost 100x this year's projection.

At Thursday's quote of $109.14, FB was selling for about 73x next year's GAAP estimate, which assumes a better-than-36% bump in earnings per share. At that price, FB's earnings yield (defined as the inverse of its price-to-earnings ratio) offers just a 1.37% return on current market capitalization for 2016.

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Value Line assumes that Facebook can grow EPS to $3.10 over the coming three to five years. It realizes the stock's very elevated multiple cannot endure for that long. Even 182% long-term growth might not justify much more than FB's Nov. 11, 2015, price. As of Nov. 4, 2015, Value Line's midpoint 2018-2020 projection came to just $107.50.

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Any disappointment might make even that range unsustainable. Profits could fail to live up to expectations and the company's P/E might not hold at 35x. A simple change in mood could knock FB for a loop. Applying a generous 50 multiple to 2016's $1.50 GAAP estimate only would support $75 around 12 to 15 months from now.

Dreamers are going to keep fantasizing about how great things could still get. Insiders and realists are busy taking profits while the glowing haze of non-GAAP growth continues to cloud visibility on the true worth of the stock.

If you are lucky enough to have caught Facebook's rising tide, don't overstay your welcome, no matter how perfect the water feels right now. Otherwise, the rip current may pull all your gains back out to sea.