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A few years ago, I found myself in an art gallery, alone, standing in front of a mural whose words I found moving. Before I even read to the end, I had reached for my phone to tweet an excerpt.

Obviously, upon realising what I was doing, I swiftly put the phone to much more sensible use, summoning a trusted friend to come round and strike me in the face with a blunt instrument for being such an unbelievable tosser.

But it made me realise how automatic the urge to share is, and how essential to the enjoyment of good things. "Happiness quite unshared can scarcely be called happiness; it has no taste," wrote Charlotte Bronte, long before the advent of peer-to-peer platforms and the like.

Sharing is the story of this century.

The geographical spaces between people have been shrunk by technology to a hair's breadth. A harpsichord fancier in Toowoomba – once thought an oddball – can now happily share plectrum tips online with fellow enthusiasts in Ottawa or Hong Kong.

Files, software, music, news, recipes: All can be shared with little cost to the sharer or recipient, a formula which gives crippling heartburn to the industries which once depended very comfortably on selling this stuff for money.

Over-sharing, in fact, is rife; the vast galaxies of Facebook and Instagram and Twitter are infested with emotional space-junk emitted by people who could probably, on balance, just have kept it to themselves. Looking at you, Shane Warne.

But the "sharing economy" is moving from information to real stuff. Sharing rooms is a thumping great business thanks to Airbnb, sharing car rides is possible through Uber, and enterprises like Open Shed and Airtasker share tools and labour.

The Australian startup TuShare has now created a network through which people with stuff they no longer need can pass it on to someone who does.

Their competition isn't retailers or eBay. It's the bin, which is where people tend to stick things they've finished with. Australians are the second highest per capita producers of municipal waste in the world, sending 690 kilograms per person to landfill each year.

Today being Global Sharing Day, TuShare is staging a "flash sharing" event online in which they hope 5000 items will change hands – clothes, toys, equipment – over five days.

Sharing makes people happy. The receiver is pleased to get – for free – something they need. The giver feels pleased to have helped, and experiences the warm glow of satisfaction experienced by people who have found someone's lost dog, or given away home-grown tomatoes; the nourishing, soupy byproduct of kindness.

According to the 2013 World Happiness Report, helping others is one of the largest factors happy people have in common.

And yet, such enthusiasm does not extend necessarily to all sharing.

When Essential Research polled Australians after the federal budget, the company found – in line with other polls – that the budget in general was about as popular as trench foot. But a couple of measures met with approval. The most popular, at 64 per cent, was the freezing of foreign aid, a measure which saves Australian taxpayers $7 billion on paper over the next four years.

Foreign aid is the most overt act of sharing that nations do. Both Labor and the Coalition committed, in the year 2000, to the bipartisan aim of lifting foreign aid spending to 0.5 per cent of gross national income by 2015. But both parties – first Labor, and then the Coalition – abandoned that pledge.

Australians like sharing, and they dislike broken promises, but the foreign aid decision is one that neatly bucks both those trends.

The Australian businesswoman and aid entrepreneur Audette Exel, writing on Thursday for Women’s Agenda, asked: "I sometimes wonder when and why the concept of sharing, which we teach our children so early on, took on a different, more negative connotation in the adult world. I watched with amazement a few weeks ago as a couple of mums were sitting in a coffee in the park with their kids, and speaking loudly against 'bludgers', 'illegals' and 'the welfare state'. At the very same moment, a child wandered into the group, attracted by the array of the toys on offer. When one little boy reached to protect his toys from this newcomer, the mothers turned in unison to scold him for not sharing."

Perhaps there are two types of sharing; one that is convenient and cheap for the giver, like handing on a bulky piece of baby furniture or sharing a picture of something beautiful, and one that requires sacrifice, like giving away part of your salary, or sharing your time to help someone else.

"A bone to the dog is not charity," Jack London once wrote.

"Charity is the bone shared with the dog, when you are just as hungry as the dog."

Annabel Crabb is a writer and broadcaster for the ABC.

Twitter: @annabelcrabb