That's a propaganda to make people become employee in their whole life because they keep thinking, if they lost this job, they won't get another one.
Most of the time, if you search other jobs when you still have your current job, you can't change your career. So let's say you're a welder, your top job would be an underwater welder. It's because you have no time to learn other skills and you're already tired.
Only brave people can earn much money, like people invest in something, they spend money to get money. People need to have their own "roadmap" instead of worrying to lose their main job.
It’s hard to leave your current job when you have a family to feed, I’m really guilty on this thought. But unless you won’t start taking risk, you won’t land into another, your dream job that pays over the other job. However, this is quite easy to say but actually hard to do when you’re in the real situation. It’s easier to just add another income than to completely quit from your job.
But if your current job is not giving you good health, you can resign from the Job even though you have not gotten a new job, if you die today your family will survive. We need to consider our happiness or good health before we remain in that current job to search for another job. That is the fact about the situation of taking risk to a better job because you will have double mind set, if I leave the current job to another job and you discover is not paying well like your previous job or you leave the Job to another job and you discover the new job is paying well more than your previous job and it will be difficult for you to make a good decision at that moment. Those that survived in adding income will tell you was not easy with them, because they have some challenges they face before they overcome the situation to become successful.