Jack Dorsey spends his mornings running one of the world's most influential social networks.
Then, at lunchtime, he springs up from his desk, walks a short way down Market Street, and takes charge of one of the world's biggest payment firms.
Just imagine that. Running both Twitter and Square must surely make Dorsey one of San Francisco's most under-pressure chief executives - an inbox chock-a-block with to-dos.
Many people said he wouldn't be able to do it. Indeed, when Dorsey returned last year to Twitter, a company he co-founded, it was only meant to be a temporary measure.
But eventually, the board came to the conclusion that if anyone was capable of reversing Twitter's fortunes, it was Jack Dorsey, even if they only had 50% of him.
140 characters is dead, long live 140 characters
It has been almost a year since he regained control of the company, and his most pressing problem back then still faces him today: fix Twitter.
"We're making progress," Dorsey told me, adding that he considers the most important thing to be the company's ability to devise, develop and release updates to the service.
"That's going very well, but you know, things take time to change."
Unfortunately for Twitter, the 300 million or so people who use the service at least once a month don't always take well to new ideas. One recent furore, for instance, was about an icon changing from a star to a heart.
And Dorsey's personal delivery of an announcement this week was designed to publicise that work was being done to make Twitter a simpler place to spend time on the internet.
But at the same time, he needed to stress that Twitter wouldn't be changing so much that its current, fiercely loyal users would feel alienated.
The "new" tweets, in which users can add photos and videos without using up any of the 140 character limit, seem to have found that delicate balance.
But improving simplicity isn't even half the battle for Dorsey.
Twitter, you will no doubt have noticed over the past couple of years, has become a service synonymous with online abuse.
That may be an unfair tag to load onto Twitter, but the ease in which people can sign up - coupled with a lack of a Facebook-style real name policy - means anonymous, hateful comments feel more commonplace here than elsewhere.
Whether a public figure or not, those caught in the middle of a controversy can find the speed and frequency of replies overwhelming, and for some, pretty terrifying.
"I don't think the negativity and the abuse and harassment is unique to Twitter," Dorsey says.
"I think it's an industry-wide, internet-wide issue that we all need to solve. And we did make it a priority for the company."
He went on to outline the company's tools for blocking and reporting abusive users.
But it's in this area that Twitter has many users unconvinced.
Those who have been at the receiving end of abuse wonder how it can be that, after 10 years, Twitter's engineers are yet to devise ways in which abuse can be proactively stopped from reaching those being targeted, rather than relying on reactive action.
One popular suggestion - giving users the ability to automatically ignore messages from accounts that have only just been registered - remains ignored, for the time being. Dorsey lists safety as a priority, but you could argue it should be the priority.
What Twitter does have going for it, of course, is that an awful lot of people would miss it were it to disappear.
Regardless of the looming threat from "cooler" networks like Snapchat and Instagram, Twitter for now remains the world's watercooler.
But how much is that worth? One easy way to alleviate the pressure on Dorsey and his team would be to sell-up. Predictably, names like Google and Facebook spring to mind.
"We're focused on making Twitter amazing and making something people want to use every single day," says Dorsey, avoiding the word "no".
Is Twitter for sale?
"We are an independent company and we're thriving and we want to continue to build that."
Even if Google came to him right now with its chequebook?
"We're focused on building our service."
Since 2014 Twitter's stock price has dropped from an all-time high of $69 (£47) to, at the time of writing, $14. It surely can't go much further south without someone making an offer he can't refuse. Get more info here...