There aren’t a fixed number of jobs. Everyone who has a job and produces things generally also creates jobs by consuming things (or by putting the money in the bank and having someone else borrow and invest it). It scales with the working population, otherwise we would have run out of jobs a long time ago. There are other reasons for problems with unemployment/underemployment.
In the case of my mailman, there is. If he retires, another person is hired to take his route. This is the case with many jobs. Clearly I'm not speaking about ALL jobs, just as when I posted the comment about the students who didn't get a job after college that I wasn't talkin about students who got a degree in basket weaving as another posted suggested. I shouldn't have to explain that my comments are not meant to cover ALL situations.
But he also creates jobs by spending the money he earns (or giving it to his family to spend, or putting it in the bank for someone else to borrow, etc).
In the great depression there were lots of people who weren't working, but that didn't somehow create more jobs for everyone else. People not having a job creates less demand, which in turn creates fewer jobs.
Sure for any one job at one company only one person will fill the position. But it's one of those things that's true at an individual level but works differently at a country level. Like if you got a million dollars it would be great, but if everybody got a million dollars it would just cause inflation. How easy it is to get a good job is determined by big things like fiscal policy, interest rates, technology, regulations, etc and not who is taking any single individual one.
Having people who want to work not working (even old people) generally isn't a good thing, it doesn't create more jobs available overall (since demand is reduced) and the remaining working people have to pay to support the unemployed people with taxes etc.
