The mistake that my parents did was trusting the hired manager too much, always be on your guide when running business and paying people salaries, people are like termites, what you paid them might never be enough for them, they will start planning to drain down your business and if you are too relaxed it won't show until it's too late.
This is a common mistake people make because when building a business, they trust others to manage it, and conversely, there's no specific control in place, so bad things can happen at any time. A business without our involvement will actually be problematic because we lack control, and others can exploit the situation for their own gain. I often hear of people who fail in business because management is delegated to others, and the owner prefers to be called the boss without being involved in the business's development.
If the majority of people believe that a business can be managed by others, perhaps the system needs to be changed, and they need to be involved in the system as controllers, especially regarding financial management. Without that, I'm not sure the business can thrive because others can cheat, ultimately leading to financial problems.