I've had two startup attempts so far.
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The first was very short lived. Not much to say. Back in undergrad, a few of us had a pretty good idea for a service having to do with overseas communication. We invested a bit of capital and time, and then we found out that the fucking USPS already provided that service. We decided to back off.
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On the second -- I don't want to say too much in public. But a few other folks and I conducted some research, which culminated in a piece of software and a patent filed for the idea underlying it. A particular research-oriented, for-profit network had provided raw data for us to use.
Our team decided that the idea had commercial potential. We got our shit together and lined up a very detailed short-term plan, including testimonials from organizations who pledged to purchase licenses for the software upon release, timeline for expanding the software and our suite of products, and so on. We pitched the thing and won the grand prize at a pretty well-renowned startup competition, which kickstarted our company.
We were going well for a while, but things went to hell when the network laid legal claim to part of the work -- and to the patent. Long and short, the legal implications of whether or not they had such a claim were huge, and so that needed to be resolved before we went balls-out in marketing and selling, lest our ass get bitten somewhere down the road.
They didn't have a claim on account of their particular contributions and what we had patented in particular, but the fact is meaningless unless it's officially really real legally backed up for real. And it turns out that legal fees are a total bitch. Want to communicate, negotiate, or otherwise talk with another party? If they put up a lawyer, you need to put one up as well. Want to check on the status of your own patent filing? You need a fucking lawyer to do it for you. Want to so much as breathe a wor-- well, you get the picture. In the process, legal fees ran us completely dry, because it turns out that huge networks can play the endurance game better than a startup can.
That was pretty much the factor that led to the eventual dissolution of the company, but there were others as well. A distant second is that, although we all busted ass throughout and wanted to see the thing succeed, my heart wasn't completely in it -- I (rightfully and thankfully) personally prioritized my education over the company. Among other things, it was exhausting pulling all-nighters digging through email chains to try to find evidence.