The job as we think of it today is a relatively modern invention. It protects you from the daily ups and downs of business. So if you’re working in an office as a graphic designer for Coca Cola or you’re a shipping clerk for some stationary manufacturer, you don’t wake up every morning and find out based on the weather or based on the market whether you have a job that day or not. You have a long-term commitment that obviously can change, but you have this buffering, this safety from the chaos of the marketplace.
And also in the modern job you don’t have to be proving worth all the time. You maybe don’t have your best performing day or week, month, but you’re not going to get fired. You just go in, put in your hours and you’re still going to get paid. There is decades of fascinating studies of how expensive it is for companies to actually monitor each worker. It’s really efficient not to make sure each worker is maximally efficient: you just hire a whole bunch of people and figure some will work really hard, some won’t work at all and most people will be somewhere in the middle.