When you see a rich man who suddenly becomes poor or an average man who never grew above his current financial state, it's basically because they possibly weren't accountable for the money that was coming into their hands.
Many factors can cause a rich man to lose his wealth besides financial accountability. Wrong business decisions, loss of job or contract, shacks or scams, health problems, government policies, natural disasters, conflict or war, etc could destroy the wealth of the most prudent people.
If you don't take your financial accountability seriously and want to allow everything to fall into place by chance, you will learn a hard lesson the bad way.
Spending without a plan or having a budget is one of the reasons why people mismanage their money. Financial accountability is the ability to use funds in a manner that you can give a detailed report of how you spend the resources. Funds shouldn't be spent recklessly because we are not accountable to anybody. We should know that we must account for our wastefulness or prudence in the future. I know a cousin who was lavishing all he earned as a seafarer on clubbing and women. He failed to enrol for advanced courses in his field while other staff spent money and upgraded. The company later did a staff evaluation and laid off all staff who didn't upgrade their knowledge. Today, he is still unemployed and looking for a means of going back to the marine academy.