When managing a large company, it’s crucial to know who does what and which divisions perform which tasks.

Bob Iger and Elon Musk both hit the ground running with their respective businesses, Disney and Twitter.

They’re both making changes as fast as they can.

One is being cheered on by his employees. The other, not so much.

The inescapable takeaway: It’s crucial to know what you’re doing.

Iger, who ran Disney for 15 years before stepping down last year, needed little catching up after the company’s board ousted his successor-turned-predecessor, Bob Chapek, and restored Iger to the top spot.

Iger wasted no time in starting to dismantle Chapek’s reorganization of the company.

“The speed at which Iger is hurtling is especially remarkable given that Disney’s board only made its overture for Iger to return to the embattled company on Friday,” CNN reported.

And why not? Iger knows most of the players at Disney and how the various divisions operate. His long track record of success has employees open to change.

Musk, meanwhile, waived due diligence as part of his $44-billion (reluctant) acquisition of Twitter and seemed surprised by the impact his immediate decisions were having on operations.

Wary employees first faced the layoffs of about half the workforce, and hundreds more then departed after Musk demanded they commit in writing to long hours and unpleasant conditions.

One of his biggest missteps was the introduction of an $8 monthly fee for some services, including verified accounts meant to deter imposters.

The move quickly prompted many people to pay eight bucks and open imposter accounts. Some were just for fun, such as the many that mocked Musk himself.

Others were more troublesome, such as one that passed itself off as the drugmaker Eli Lilly and declared that insulin would now be free. Lilly lost millions of dollars in market valuation.

Musk tweeted Monday night that he’s shelving the subscription plan until he figures out how to deal with the problems his solution created.

All the confusion at Twitter could have been avoided if the new CEO had just taken the time to learn more about the company he’d purchased. Instead, he’s making mistakes as publicly as possible.

Obviously not all CEOs benefit from Iger’s past experience. It’s unusual for a former CEO to be asked to return to the driver’s seat.

But this is a guy who understands his business and has the support to execute bold moves.

Musk will get there; he’s no dummy. But his impatience to act before doing his homework shows him to be impulsive, impetuous and insensitive toward underlings.

Future CEOs will look back on these two corporate leaders. And they’ll hopefully learn some valuable lessons.