Twenty years ago yesterday, I had my last alcoholic drink, if you don?t count a couple of beers 11 years ago that I consumed on a test basis, and which made me seriously unwell. Abandoning the booze is one of the things I got right in my life. This seems like a good week, however, to talk about mistakes.

To err is human, to forgive divine. I made a mistake last week in trusting someone who had never let me down before. It cost me $6,000.

When I used to speak publicly on the subject of finance, I would counsel people not to make what I called the ?$3 mistake?. The idea was that you were free to make whatever financial mistake you chose, so long as it didn?t cost you more than $3. I spoke one day at Bermuda College to a group of retirees, and ran my theory by them. They were less than impressed. Being retired, and being Bermudians, they all had serious savings, and would have quite happily used three dollar bills to light their cigars.

Had I better qualified the audience, I would have known that the rules that applied to my impoverished condition would not apply to theirs. The advice was good; the scale was wrong. What those people needed to do was to avoid making mistakes that cost $3,000, not $3.

That was a long time ago, back in the days when I tried to drink every bar in Hamilton dry whenever I left the house. Now, I have changed the rule in my case to $300; I try not to make mistakes that cost more than $300. Obviously, I try not to make any mistakes, but when I do make a blunder, I try to keep the cost under $300.

You?re going to have to adjust the numbers to suit your own circumstances. Depending on how well off you are, try to limit the cost of your mistakes to $3, $300, or whatever number - three plus the relevant number of zeroes - that applies to your economic situation.

By ?mistake?, I mean any action that ends up costing you money that you would rather not have spent. I?ll use $300 as the illustration for the balance of this article, and let you add (or subtract) zeroes to suit yourself.

If you buy an outfit that costs $300, and when you get it home, you hate it and vow never to wear it, think a little harder before you buy the next one. The rule is to apply extra care to any decision that is going to cost $300 or more, because the money you lose is just as important as the money you make. Think about it for a second. You?d gladly do an hour?s extra work for $300. Losing that much in five minutes through your own stupidity should make you miserable.

This is not as easy as it sounds. Heading into last week, I had no idea I was about to suffer a catastrophic loss. I gave up part of my vacation, thinking I might make some money and have a wonderful time. Although I relied on someone else, who let me down, the fault remains mine, because I trusted, rather than double- or triple-checking. Other people?s mistakes can be just as costly as your own. If you lose $300, whose fault it was won?t make any difference to your bank statement.

Having made a mistake, there are only two things you can do, if the error can?t be undone. You can suck it up and get on with it, and you can learn from the experience. In future, will I trust the person whose incompetence let me down? You bet I won?t. Will I look before I leap into a similar situation? You can bet I?ll try. Has the whole thing ruined my life? Nope. I made a mistake; I paid the price; and now a new week has started. Plenty of new mistakes to be made, no doubt.

Such stoicism gets easier as you age. If last week had happened to me when I was 25 years old, I?d have been boiling about it for months, and I would probably have gone to great lengths to get my own back. Now, I?ve got other fish to fry.

The message, I suppose, is that you have to watch your own back, because no one else will. As hard as you might try to earn and save money, make sure you bring similar discipline to the money you do spend, and the activities you enter into. Don?t let your caution stop you from doing things; just think twice before you act.

If you have the impression that I?m talking to myself as much as I am to you, you?d be right. I really took it in the neck last week, and as mature I am suggesting I might be, it still hurts. I was taken for a sucker and the person who did it then compounded matters by broadcasting the mistake as if it were entirely my fault, to anyone who?d listen (and, apparently, several people who wouldn?t.)

But I am going to take my own advice, suck it up, and get on with my life. One thing I do know: I won?t make that mistake again.