Investors in fintech company Square don't seem to approve of the departure of CFO Sarah Friar, but CEO Jack Dorsey certainly does.

On Thursday, Square's stock plunged by as much as 16 percent before rebounding with a 7.2 percent gain on Friday, as markets reacted to the news that Friar was departing to become CEO of Nextdoor, a social network that helps neighbors communicate with each other. Yet on Friday, Friar shared a personal message that Dorsey — who also sits at the helm of Twitter — sent her applauding the decision.

Analysts and tech insiders saw Friar's departure as a major blow to Square. Friar was viewed as a particularly effective second in command, though Dorsey said this week that no one executive is responsible for execution at the company.

However, Twitter's chief used the occasion to gave his protege some sage leadership advice.

In a screenshot of an iPhone text message captured by Friar, Dorsey imparted three suggestions that amounted to career counseling for the newly minted CEO. "In considering what you're about to take on, I believe it's best to highlight some challenges you'll likely face. I have no doubt you'll be able to overcome all," Dorsey wrote.