After a while you loose the ability to view your business from the customer's perspective because you rarely associate with them. Then there's your family life to consider. You can easily find yourself leaving a lonely spouse at home and rarely seeing your children. I don't have any statistics on marriage breakdowns in this industry, but I bet the figures are high. Just among the owners and managers I know and work with the record is appalling.
Alcohol is the next big problem.
I've worked with a few very sad examples and seen quite a few others well on their way to developing a debilitating or mortal habit. In fairness, lest you think I am preaching from a pious position, I should tell you that I have had to curtail my own drinking a few times. It's easy to slip into the habit of having one or two every night after close. Then it becomes one or two with good customers, a glass of wine with dinner, and so on . . . Then we have rich food in abundance.