There is however an opportunity cost for being rejected a 100 times: the time spent applying could have been spent on starting a business or other activities.
Starting a business, is ofcourse, another way to get rejected. I think this post is more about leaving your comfort-zone in the face of fear or anxiety, and not so much about getting a job.
Worse still, an opportunity is "spent" with each rejection.
This is only a problem if you believe that there is a limit to opportunities. There's always another opportunity around the corner that you haven't seen yet. And sometimes you have to fail at the obvious ones to see what the correct one is.