My sister finally repaid me for a loan – do I tell her she gave me $100 too much?

My sister has owed me money for years. After finally paying it back, she unknowingly paid an extra $100. As she’s been ungrateful throughout the years, is it wrong if I return the $100 in a card for her coming birthday?
J.O., Ballina, NSW

Credit: Illustration by Drew Aitken

Let’s imagine a scenario in which you didn’t loan that money to your ungrateful, money-hogging sister, but instead left it in the bank in your everyday transaction account. Well, at the end of several years, your money would have increased in value by a whopping 0.0000000 per cent per annum. OK, not amazing, forget about banks. Let’s say you invested that money in the sharemarket, maybe a reliable, blue-chip stock such as Telstra. Well, over the past few years, you would’ve raked in a very tidy profit of minus 2.5 per cent. All right, the sharemarket, bad example. What about other money-making opportunities? Real estate? Struggling. Crypto? Too volatile. Bonds? They’re undies (and, anyway, Tradies has pretty much captured the market: less chafing, roomier crotch pouch).

You know what? By some miraculous accident, you seem to have discovered the canniest investment strategy in the Northern Rivers region of NSW: putting your money into Ungrateful Money-Hogging Sister – or, as she should be listed on the Australian Securities Exchange, UMHS.AX. Now I may not be the most money-minded genius around; I once invested in cheap biopharmaceutical shares just in case a deadly superbug wiped out most of humanity – and when COVID-19 almost did, I made nothing, which was extremely disappointing. But after hearing about your financial success, I would happily invest in UMHS.AX, so if you could forward her personal details, I’ll get onto the paperwork.
Meanwhile, keep that extra 100 bucks; you’ve earnt it. But maybe throw her 10 per cent as a brokerage/birthday fee. I don’t know what that amount is. You can work it out.

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