No matter how hard leaders may try, they cannot expand the number of hours in the day. When leaders take on more than one job, it is inevitable that others will question whether they can cope. Jack Dorsey, who is chief executive of both Square and Twitter, is the latest to come under the scrutiny of external time-managers, in the form of Twitter investors.

Hedge fund Elliott Management is questioning whether the “part-time” chief executive is distracted.

Scott Galloway, business school professor and Twitter shareholder, has also drawn attention to Mr Dorsey’s ambition to spend some months of this year in Africa. “It’s a 9-hr time difference from San Francisco to Nigeria — so for pressing issues, the CEO will literally be asleep. How will absentee leadership affect employee morale and stress levels?” Prof Galloway asked in December. Mr Dorsey last week said he was “ re-evaluating” his plan but defended his twin roles. Despite reports of paralysis and indecision at the company, Twitter staff have rallied round a #WeBackJack campaign on the social media site.