So, if you do choose to return a trolley, you are doing so purely from your own desire to do what's right. Or, perhaps, a touch of shame – you don't want anyone you know to see you acting selfishly after all.
The shopping cart theory proposes that doing the right thing, without any benefit to yourself, is the mark of a good person.
But I would go further than that. What lies behind "goodness", in my opinion, is the motivation – if you are doing something out of obligation, reward, or social mores, that tilts a good deed towards being self-serving.
Conversely, what is it that makes a bad person? Their bad deeds, the harm they cause others? Someone who can't reflect on their actions and change for the better? Someone who knowingly inflicts pain? Selfishness?
In many ways, goodness and badness are fluid concepts. Humans are not black and white, good people do bad things and vice versa. We're all shades of grey.
Mother Teresa illustrates this. Her very name is a byword for goodness, the woman is known for dedicating her life to helping poor people, even receiving the Nobel Peace Prize and being canonised after her death.
Yet her reputation is controversial in some circles – she was dogged by accusations of misuse of funds, poor medical treatments and religious evangelism throughout her life and beyond to the current day. Even literal saints have shades of grey.
And that's just it, isn't it? We're all complex creatures with motivations that can change from one moment to the next. We can be the kindest person on the planet 99.9 per cent of the time, then in a one-off fit of pique, we're rude to someone and forever leave that one person with a bad impression.
I try to keep that in mind when I encounter "bad" people in real life.
My toddler is a people magnet. His soft curls, his wide smile, and his loud singing and story-telling voice attract notice, usually friendly.
I can't walk anywhere without people approaching him. It's adorable.
One such occasion happened last week while doing the groceries. I was looking at the muesli bars while the little one recited Scuffy the Tugboat.
An older man approached us, firstly admiring the famous curls and then striking a conversation about my boy's interests. Nothing out of the ordinary – until my boy let out a phrase that seemed to deeply offend the gent in question.
"Ka pai!" my toddler beamed at high volume. The gent gave me a disgusted look, barked "I don't want to hear any of that!" and abruptly marched off.
I continued shopping, containing my laughter until I got home and regaled my husband with the tale of the crotchety old boomer who can't handle a little te reo.
That man made an impression on me, one that will forever sit in my memory as an encounter with a bad person.
For all I know, he could be a generous person who volunteers at a local charity, tips all his waiters, and always returns trolleys when he's done with them. But that one moment of racially-tinted rudeness will always taint my impression of the man.
Contrast that with another experience I had this week, again with my radiant toddler.
I asked the little guy what he wanted to do today: "Café!" he reckoned. He's so bougie.
So off to his favourite café we went. As we walked in the door, I realised I'd forgotten my wallet. I double-checked and, sure enough, no eftpos card. Bugger. I told the little guy as much and turned to leave – and was stopped at the door by a beckoning woman. I looked at her trying to figure out if I knew her from somewhere but didn't recognise her face. I warily wandered over.
"I'll pay for you. Here, I'll give you some cash to get your food."
My goodness. I tried to turn her down, but she was insistent, in the friendliest way. I genuinely teared up at the sheer kindness of her gesture. I ordered our food, returned the change and thanked her profusely.
This time, I raved to my husband about the generous woman who absolutely made my and my toddler's day with a small act of kindness.
Maybe, just maybe, this woman is a nightmare in her everyday life. I doubt it, but it's a possibility.
But when a person is kind to someone they will, in all likelihood, never be seen again, that speaks volumes about their character and inclines me to think they are an overall good person.
Or maybe after a yummy apple and walnut muffin, I'm a bit biased.
I bet she puts her trolleys away.
Sonya Bateson is a writer, reader and crafter raising her family in Tauranga. She is a millennial who enjoys eating avocado on toast, drinking lattes and defying stereotypes. As a sceptic, she reserves the right to change her mind when presented with new evidence.
