What drives people to build, make and experiment to create new things? Some people are driven to solve a problem that faces humanity; they are driven to make the world a better place. Two examples: Bill Gates wants to rid the world of malaria and so is throwing money at the problem. The team behind the citizen science project SpaceWarps (http://spacewarps.org/)) are driven to find out large scale things about the universe and so is trying to engage the public in processing the data to allow further measurements.
I wish I had such lofty goals; mine are far more selfish.
I don’t particularly want to be remembered (although it would be nice!), I want my finite time on Earth to have made a difference. I also want to have fun doing it.
That sounds very grand, but it’s not really. It just means that I want to leave a mark that will inform future generations, and possibly inspire current generations to do stuff, whilst having doing something I enjoy.
Whilst I was doing my GCSEs, in my English Language lessons I wrote a short piece of fiction about a detective investigating a murder in a train tunnel. In that, the detective expounded about how nothing really mattered as humans are just bags of cells operating to reproduce the DNA. It was a distilled version of the ideas from Richard Dawkin’s book The Selfish Gene, which, as a precocious teenager, I’d been reading . My teacher at the time declared (without debate) that it was a “marvellous pastiche” because such “extreme views” wouldn’t be held by normal rational people, and so gave it top marks.  Unfortunately, it wasn’t a pastiche. I think that we are just self replicating bags of meat, with the unfortunately side-effect of conciousness.
However! This doesn’t mean we can’t do useful things. We clearly can build things that outlast us. Brunel built tunnels that are still used today (the Thames Tunnel for example) and had fun doing it; Box Tunnel is allegedly deliberately aligned so that a shaft of light shines through it on his birthday. (Although, according to Wikipedia “Brunel is credited with turning the town of Swindon into one of the largest growing towns in Europe during the 19th century”, so it wasn’t all good.)
Some may say that this gives us license to be entirely hedonistic. In the short term, yes. But in the longer term, if we took the entirely hedonistic view, there is no requirement to hope that future generations will benefit from our lives.
Initially, I wanted this to be scientific knowledge. I have written, and contributed, to papers, and so have helped the sum total knowledge of humans increase. In a hundred years, my name will be found in copyright libraries where copies of these journals will be found. So, done that.
Second option is to have kids. I have kids, and they are wilful, fantastic people who, hopefully, will remember their Dad.
Third option is to build things. I’ve been lucky enough to get involved in building “general purpose” scientific instruments that will help others find out things (the the parlance, they are “common user” instruments) as well as more specific instruments that will measure a particular quantity to high accuracy. I have found this one the most satisfying. These instruments can take many man-years to put together, and so can seem frustrating during the process. Looking back, it can be worth it. Because of the very long time scales involved, it can be fun to throw together a shop-bought kit to produce something over a weekend or two.
To summarize: We build things to give our lives meaning whilst enjoying ourselves.
To summarize the summary: Because it’s fun.
 This dates me. And probably geographically places me. Fine
 As a piece of fiction, it’s an idea I want to return to.
 Had the debate happened, I would have probably not got top marks.
 I am writing this with a beer by my keyboard.