A company (an employer) rents the time and skills of employees for a particular task. It's not a pool of work that employees must struggle to achieve regardless of circumstances - it's the employer's responsibility to hire enough staff.

For example, my paternity leave (20 days or 40 half days) would not impact my colleagues. Some of them can opt into overtime, but the same labor laws also define how overtime works - as an employer, you can't order someone to work extra hours unless described in their contract (and limited to the maximum specified by law, with mandatory regular breaks). Overtime is also paid at 150% or 200% of your regular pay, depending on the day of the week and hour of the day (e.g., weekends and nights obviously cost more than daytime rates). Very few jobs are even allowed to work on Sundays.