When the business can't open without you.

My career is one in which, if I am suddenly ill, a replacement must be found or the business can't be open. At all. This puts a great deal of pressure upon a person to come in to work even when ill. There is an expectation that, unless you are incapacitated, you will come in. Once you are there, an effort can be made to find someone to come in and replace you, if you are really sick. But it is bad form just to call in and not show up. Most people in my situation will haul themselves out of bed, show up when sick and try to make it through the day.

Many support worker will also come in when sick. This is not office work, it is providing a service that has to be maintained throughout the day. Every worker knows that, if they don't come in, there's a possibility that the business will not be able to replace them and business (and the business's reputation) will suffer, and may explose other workers to customer complaints.

It is hard to take a day off sick. Paid or unpaid sick leave, it really wouldn't make a difference to the work ethic of my job.