So many white collar office jobs pay well, but a large portion of their "work" is sitting in meetings, sending e-mails to each other, creating useless reports, etc. And people think that's "going to work"! Just wait until the bubble pops (which could be any week now), those people are going to be in for a rude awakening.
If you can't make something or fix something, you're not useful and no one will trade you the value of their own work (food, medicine, clothing, services, etc.)
There are many things you can make: chairs, tables, houses, tools, computer programs, websites, graphics, tax returns, Excel spreadsheets full of sales records (accountant), a healthy baby delivery (midwife), a person to look good (barber, beautician), etc.
There are many things you can fix: souls (priest), bodies (doctor), houses (handyman), cars (mechanic), software, plumbing, electrical, driveways, foundations, etc.
The first level of "useful" is providing a good/service that people need TODAY.
But not all careers are similarly future-proof. For example, in a depression or collapse scenario, people have MUCH less money, and they will be cutting back on things like dining out, having their nails done, etc. even though those ARE concrete things/services you were performing, which could make a living in 2015.
Many home businesses will either go out of business, or the mom & pop owners will just have to hustle that much more -- including doing their own accounting -- to make ends meet.
But some things can never be done away with or replaced -- food, shelter, clothing, medical care. Those are the safest careers to be in.