Realistically, 1 person missing from a small business can mean 10% of their workforce is gone - and due to the size of the company they may not have people to cover the missing staff.
10 people or 10,000 people, if you can't afford your staff going on parental leave / long term sick / vacation, you don't have a sustainable business.
You've never run a startup or small business. At the beginning margins can be razor thin, and unplanned or extended leave can have a huge impact.
If you run a business on the assumption that you're going to have all your current employees working for you continuously for the foreseeable future, you're going to have a bad time.