I am in my mid 40s. My generation was not taught to share, unless it was within the family, with your siblings. On the contrary, there was a strong emphasis on individual enjoyment of resources. Learning? At school you would be evaluated individually, and explicitly forbidden to collaborate with others on assignments and tests, a practice called “cheating” by teachers. Work? You would apply for jobs, individually. You would receive a salary in return for participating in a hierarchical command-and-control structure, the whole point of which is that you are a cog in the machine, and as such you have nothing you could possibly share. Housing? You should aspire to a nice apartment for yourself and your family, in which you would share with your neighbours only the staircase. If you were more affluent, even better: you were encouraged to go for an independent house, with your own fenced garden and no sharing at all.
This left only two arenas: science and the Internet.
I had the good fortune to do science (economics) in the early 90s. I now realize there were contradictions about sharing in academia: you would publish results, but not necessarily raw data (unless it was needed for referees to review your work). You wanted your work to be widely spread, yet publications would be copyrighted by default. But what struck me at the time is that anybody agreed that there was no way that even the most brilliant mind would achieve anything without leaning heavily on the work of others. It was natural to think of knowledge as a big heap of thinking and results. Everybody took freely from it and gave back to it. Everybody, that is, save the very top people: the pinnacle of scientific success was still Craig Venter, heavily funded by corporate finance, sitting on a big pile of proprietary genomic data and using them to churn out patent (privatized knowledge again) for Big Pharma.
The Internet taught me the bounty that can result from sharing with strangers. It started opening up my band’s website to unmoderated comments in 1998 and being flooded with love; it continued in the early 200s with web 2.0, and particularly blogs. Blogs became very important in helping me to find knowledge I could then absorb and redeploy in my own projects. I wanted to take part in the online conversation, and to give something of my own back to it. So, in 2005, I took up blogging too, and have not stopped since. I immediately discovered that - though reading blogs can be fun and very instructive - it is only when you are a full participant in the web of online exchanges tat you can make the most of it. If you publish good stuff people will notice: they will leave you comments, be inspired by you to write their own content, and recommend you to their friends. This was a complete game changer for someone like me, who was not embedded into a top university: as if by magic, suddenly I was coming across knowledge that was 100% relevant to me - I would even say necessary - without any effort. Most of it was so knew that it would not hit the journals for years yet. My learning speed doubled, as almost all time previously spent looking for sources suddenly became available for reading.
This is possible because what is arcane and hard to find for you is an everyday matter for another person, and viceversa. If that person knows you exist and knows about your interests, she can send you very relevant knowledge with a click; and that click saves you hours, if not days, of sifting through libraries. And here is the trick: the more knowledge you share, the better people in your network will get at sending you stuff which is relevant for you; and the more there will be of them in your network, because people with similar interests tend to gravitate towards each other in social networks (a phenomenon called homophily). So you share: you would share it even if your motivations were perfectly egoistic. But in so doing you help others, because your thinking, obvious for you, can be very inspiring for someone else. I put a ridiculous amount of work in my blog: I have written more than 700 posts, most of them in two languages. I do it for free, and pay for the hosting and the occasional help with development out of my own pocket. It is a great investment, and I have no intention of giving it up: in fact you could say I owe my present job to the fact that someone at the Council of Europe reads my blog.
Once you learn the trick, sharing becomes quite natural offline, too. Creating club nights to build a nice hangout place for the local community; lending willingly your personal property; making the extra bedroom in your apartment available to people travelling to town; working out of shared spaces. I even wrote a book, ad somehow persuaded the publisher to put out an advanced dratf version on the web, with a Creative Commons license that makes it legal to download it and reproduce it. I have done all this, and I plan to do more in the future - for example, I really want to live in a co-housing space. But the Internet is the place where it all started for me.