David Altig, Atlanta Fed, provides the following graph (courtesy of Bureau of Labor Statistics) in his discussion of the poor outlook for employment (here).
"Underneath the usual total unemployment numbers are the reasons an individual is unemployed: You are on temporary layoff; you quit your job; you have reentered the labor market and have yet to find a job; or you are entering the job market for the first time and have yet to find a job. Or, finally, you have been permanently separated from your previous employer, who has no expectation of hiring you back.
The last category is the dominant reason for unemployment at this time. That might not seem surprising, but it actually is. Never, in the six recessions preceding the latest one, did permanent separations account for more than 45 percent of the unemployed. The current percentage stands at 56 percent as of September and appears to be still climbing:"
This means that the number of jobs that have gone away and are not coming back is unprecedented. I have read this stated as opinion a number of times, but I don't know that I have seen the data before.