Whether you're a freelance writer or Bill Gates, everyone needs a budget. When looking at your money, you should be tracking every penny you spend. Set a budget and know where every penny goes.
I personally recommend watching the little costs that we normally don't pay attention to. The $10/month accounts add up over time. The more of them you have, the more money will be going out of your account each month.
While this is a habit that most millionaires follow, millionaires in the process of going broke are not watching and following their money -- they do the opposite. They cannot even tell you where it went. These soon-not-to-be millionaires don't even go-over their bank statements or monthly bills to make sure that there aren't any unauthorized transactions. They also don't look at bills from restaurants, hotels or retail purchases, much less the grocery store, to make sure that they weren't overcharged. They also don't compare prices for items they routinely purchase, such as their cell phone bill.
In the end, these millionaires waste a lot of money simply because they don't track their spending. It may not seem like much of a problem in the beginning, but it can quickly add-up. In the end -- well -- no money is a problem.
Related: How I Run 3 Multi-Million-Dollar Companies While Getting 9.25 Hours of Sleep a Night