Then I caught myself. I gave her the $20, went on my way and - despite all my agonising over how I'd miss the money - never really thought about it again until now.
How did I get to a place where I have to mentally prepare myself to give to charity, but don't think twice about donating $50 to buy a beach in the South Island I'd never heard of before?
A Unicef video is doing the rounds on Facebook this week.
The UN children's charity took a 6-year-old actor to Georgia's capital and dressed her alternately as a homeless girl and as a rich girl. They took her out to Tbilisi's streets and to a restaurant.
Spotting a well-dressed child alone on the street, two women crouch beside her and ask if she's okay. The same child dressed as a homeless girl is ignored.
In the restaurant, the rich girl is fawned over. A man asks the staff to get rid of the poor girl. They have to call off the experiment when the girl flees in tears, because even though she knows this is an experiment, it's too much unkindness for a 6-year-old to take.
If I'm honest with myself, I would have acted like those adults. I wouldn't be able to claim a degree of humanity or empathy or generosity greater than any of them.
I'm ashamed of the video because of what it tells me about myself.
If anything, I should be opening my wallet more. The poorest Kiwis are very, very poor. Figures out this week show 40 per cent of the people in this country own only 3 per cent of the wealth.
That's very little shared between very many. And yet, half the country's wealth - 16 times more than what the poor people have - is carved up between only 10 per cent of our population.
That's the world, right? That's the difference made by hard work and initiative and determination.
Yeah, to a point. But it's also the difference made by mental illness. And it's the difference made by parents who booze instead of feeding kids. And the difference made by being unable to go to school half the week during the winter because you have to walk and you don't have waterproof clothing and wagging is better than getting sick. Again.
And it's the difference made by a country that says, "That's the world, right?"
I know in a month I'll not feel guilty any more. Life and work and friends and family will happen, and we'll forget about the 40 per cent of the country's poorest because they're not sitting outside our front doors. That, really, is the world.
So, before I forget to care, I logged on to the same Givealittle page as Lorde and made a donation. It was more than $50 and I won't even notice it's gone.