And many founders do leave companies after they're acquired to start something new.
Instagram was bought by Facebook in 2012, and now boasts 1 billion monthly active users. But now that its founders have announced they are leaving in a swirl of well wishes and vague explanations, some of the same worries are bubbling up again - and then some.
For Facebook it was an important land grab in the shift to mobile, an area that it had hitherto struggled to really grasp and a shrewd purchase of a service that could have rivalled Facebook itself.
Instagram has some inherent advantages over Facebook as far as content is concerned.
Instagram Stories have been a hit on the platform.
How does Facebook need Instagram?
Instagram had just 31 million users when Facebook snapped it up for $1 billion; now it has a billion. Facebook hasn't been cool for many years, and people have always proclaimed they were using Facebook less even as data showed they were using Facebook more.
Given Facebook's slowing growth and newer challenges, the company's leadership saw Instagram as the next obvious golden goose.
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Instagram has been a primary focus of those efforts. There are some popular features on Facebook that Instagram may be able to adapt.
There have been reports of tension between Facebook and the pair although there are no signs of animosity in their departing statements nor those of Facebook chief Mark Zuckerberg who said he had enjoyed working with them and looked forward to seeing what they build next. That changed. But so did the number of users - now more than a billion. And it was the first startup allowed to operate mostly independently.
This claim was backed by another company source, who told Tech Crunch that Facebook put pressure on Systrom to help expand the social network's dwindling teenage audience - Instagram's primary demography.
Recently, Instagram has been on a roll. It's also been a bright spot for Facebook amid a tumultuous time for that platform, which is grappling with fake news, foreign election meddling and privacy issues. And especially when its parent has long stopped being cool, what with everyone and their grandma now on it.
They are not the only creators of a Facebook acquisition to quit their creation - Whatsapp's Jan Koum left the messaging app in April.
The two had clashed with Zuckerberg in recent months, the person said.
J.P. Morgan analyst Doug Anmuth commented on the sudden departure saying: "We believe their departure comes as a surprise given Instagram's success and its growing importance within Facebook".