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.
Not entirely true, it has a deeper meaning than just for the job. It is all about having peace of mind and not being consumed by greed. The statement does not conflict with having ambition and desire to improve oneself, and it only conveys being thankful for the present and do not be frustrated if plans failed.
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.
I can say that smart and brave people are the ones who are destined to earn a lot of money. Bravery, taking uncalculated risks can only lead to financial losses. While being smart but not taking risks can only leave a person stuck in their current situation. So the combination of both qualities can synergize the positive effect and ensure that a person can avoid unnecessary financial losses.