It was a small mistake but one that cost British hairdresser and mother of two "Sally Donaldson" thousands of dollars.

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According to The Guardian, in October 2012, Donaldson (not her real name) experienced a sickening, gut-wrenching moment when she discovered that over the course of two years, each time she had transferred her monthly paycheck of $1,500 from her HSBC account to the joint one she shares with her husband at Nationwide building society, she had accidentally been placing the money in a total stranger's account. After two years, the amount she had transferred was roughly $40,000.

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"It wasn't until October 2012 that I discovered the £1,000 was not showing on our joint account's monthly statement. Having moved over to paperless statements in 2010, I had been checking that my wages were leaving my business account held with HSBC at the end of every month. However, to my horror, I now saw they had never arrived in our joint Nationwide account. Scrolling back, the last time my wage appeared on our statement was May 2010," says Donaldson in The Guardian. "I frantically checked my numbers for the bill payment scheme I had set up with HSBC and could see that, on setting it up, I was one digit out … the money has been going to another Nationwide account holder for the past two years, amounting to £26,650!"
"The payment was set up clearly to my name, my sort code but with one account number digit being incorrect…..Phone calls to Nationwide that night, many tears and numerous subsequent calls and letters, have left us with just £1,000 returned and a complete blank of information from Nationwide," she says.

It may be difficult for Donaldson to get her money back. According to The Guardian, the recipient refuses to return the money and the bank cannot reveal his or her identity due to data protection rules. What's more, British law dictates that when money goes into the wrong hands, it can be withdrawn without gaining permission first for up to six years after it's wrongfully transferred. But in Donaldson's case, the recipient had withdrawn the money through ATMs so there is nothing they can do. Shine attempted to contact Nationwide for comment but emails were not returned.

"People have become so dependent on technology that they've developed a blind trust in computers," says Manisha Thakor, CEO of MoneyZen Wealth Management. "But technology isn't perfect; when you consider the sheer volume of transfers that banks make every day, it's actually very easy for an error to occur. People have a personal responsibility to take ownership of their finances." Here's how to avoid making a similar mistake:

Communicate: It seems unlikely that Donaldson, who was supporting herself on a hairdresser's salary, could overlook the fact that her family's bank account wasn't as flush as it was supposed to be but according to Thakor, many couples don't communicate enough about finances. "What's most troubling about this story is that it occurred between a husband and wife," says Thakor. "It was a very personal transaction and would have been easy for Donaldson to check in with her husband and ask if he received the funds." Yes, a simple, "Hey did you get that huge money transfer I sent you?" over dinner could have prevented the problem from escalating. Even if one person is better at managing money—which is so often the case between couples— staying in the loop about bill paying and money transfers is crucial.

Read in reverse: When you're double checking the number you typed in, read it again but this time backwards. "By reading from the last number to the first, you'll avoid scanning on autopilot," says Thakor. "This process forces your brain to stay alert while you read so you're more likely to catch typos."