It seems to cost about $10 to 50k to acquire the tools, vehicle and licenses to start a plumbing business. Is there something else that’s substantial beyond the normal attention to detail and savvy that every small businessperson must have?
So at least sometimes, it is life or death.
A possible alternative path is to take over management of a business from its current owner, and eventually buy it out. Also, just a little bit of seed money might make the difference, e.g., buying a van full of basic tools is expensive, but it's not SpaceX expensive.
I've hired workmen who turned out to be "a couple guys with chainsaws and a pickup truck." So it might be possible to ease your way into a business by starting with smaller jobs.
And now that I say it: hospitals need electricians too. Electricity goes out in a hospital for too long, lots of people die.
And actually a third point: electricity -going out- is not the only thing that could kill a client, it's not too hard to start a fire.