Couldn't manage it.
When I was younger there are points I did have two jobs. But it wasn't a secret and was very long hours.
If you can fill expectations for two jobs at once, more power to you. I know there are jobs that are simply under provisioned out there. I've considered it. I could take two lower-mid level positions and make slightly more than the very senior positions I've been in the past few years. So who knows.
If your job performance sucks, then your performance sucks and the reason shouldn't matter.