• Instagram’s cofounders announced their plans to leave Facebook on Monday after six years with the company.
  • A close look at the “farewell letter” reveals several breaches of etiquette that suggest this is not an amicable break up.

The surprise departure of Instagram’s cofounders on Monday evening caught everyone by surprise – including, it seems increasingly likely, Facebook itself.

The farewell statement that Instagram CEO Kevin Systrom posted Monday on behalf of himself and cofounder Mike Krieger showed a complete disregard for all the usual niceties that go into these sort of things. And that’s probably not an accident.

While the average reader might not notice the hidden barbs, there are various clues in Systrom’s goodbye note that hint at the real story behind their departure, which most likely will be revealed in the coming weeks.

First, let’s take a look at the statement:

“Mike and I are grateful for the last eight years at Instagram and six years with the Facebook team. We’ve grown from 13 people to over a thousand with offices around the world, all while building products used and loved by a community of over one billion. We’re now ready for our next chapter.

We’re planning on taking some time off to explore our curiosity and creativity again. Building new things requires that we step back, understand what inspires us and match that with what the world needs; that’s what we plan to do.

We remain excited for the future of Instagram and Facebook in the coming years as we transition from leaders to two users in a billion. We look forward to watching what these innovative and extraordinary companies do next.

Kevin Systrom, Co-Founder & CEO”

Now, let’s look at some of the red flags in the announcement that tell you all is not OK:

1. Timing

The fact that the two cofounders are leaving together is remarkable in itself. And the fact that the announcements of their departures were not staggered, with a customary six week buffer to provide an appearance of stability and transition, is even more incredible. The message is clear: this was not planned.

2. Is it just me or is something missing?

There are two names you didn't see in the announcement: Mark Zuckerberg and Sheryl Sandberg. The traditional thank-you to the founder of the company may be a platitude, but it's an important one. Omitting it is the farewell note equivalent of not returning someone's handshake.

3. Time to explore our creativity ... again

The key word here is "again." The founders seemed intent on making it clear that indulging their creativity and curiosity - the lifeblood of tech innovators - was not something they could do inside of Facebook.

4. "Building new things"

Think of it as another tacit rule of Silicon Valley business. You leave companies to go spend more time with your family, to "recharge your batteries," or to collect vintage sports cars. But you don't, at least not in your farewell note, leave a company to prepare to build a new, and potentially competitive, product.

5. Timing, part two

This isn't mentioned in the goodbye note, but it's one more clue pointing to the abruptness of the decision: Systrom was scheduled for several high-profile speaking engagements in the coming weeks, including The Information subscriber summit on October 18 and the WSJD Live conference in Laguna, Calif. in November.

"The optics are so clearly adversarial," said one person close to the company. "You don't go out like that."