An employee who wakes up too sick to work still gets paid. Their salary lands on the usual day, sick leave covers the bad week, and if something serious keeps them out for months, there is often an employer disability policy waiting behind it. A freelancer who wakes up too sick to work just stops earning. No sick pay, no paid leave, no HR to call. The invoices you did not send this week are simply gone.
Most freelancers know this in the abstract and plan for it by hoping it never happens. That is a bet, and the odds are worse than they feel. The Social Security Administration estimates that more than one in four of today's twenty-year-olds will become disabled at some point before they reach retirement age (Social Security Administration). Not a freak accident. A back injury, a long illness, a surgery with a slow recovery. This is about building the safety net that no employer is going to hand you.
The safety net you gave up when you went freelance
The thing worth seeing clearly is how much an employer quietly carried. In the UK, an employee off sick gets Statutory Sick Pay, £123.25 a week for up to 28 weeks, paid by the employer. To qualify you have to be classed as an employee (GOV.UK), which a sole trader is not, so a self-employed person gets nothing from it. In the UAE, a private-sector employee is entitled to up to 90 days of sick leave a year, the first 15 on full pay (UAE Government); a freelancer, who is not on an employment contract, gets none of it. In the US, employer short- and long-term disability plans exist, but only for employees at firms that offer them, and the self-employed are outside that door by definition. Everywhere you look, the sick-pay system is built around a payslip you no longer have.