I spent 4 or 5 months last year building a website (now defunct) called undo.io. It was meant to be a hybrid of a todolist, notepad, calendar and twitter.
I did no customer development. I just wanted to build it for myself. :)
I was previously a co-founder at a successful startup in Seattle. I had a secret feeling that there was something special about me, and my next project would just magically succeed.
I came from a Microsoft background, but decided to learn Ruby on Rails to do it. Everyone kept telling me I could code things faster and better if I went FOSS.
It took me twice as long as I thought to build it. It was hard to use. It was unclear what it was for.
I didn't even really think about a business model ( I just thought - "... probably advertising" ;) )
I worked a lot, worked through vacations. My back went out. I gained 10 pounds.
Eventually I realized that there was no viable business and it was just a personal project, I shut it down and didn't do anything useful for 2 months.
Then I pulled my entire family up, moved back to California, and started again on new business.
What I think I did right
I learned some important technical skills - Ruby on Rails, Linux, SOLR, Vim, Heroku, and a few other pieces of that stack.
I didn't break the bank to do it. I kept working at another job and that made my home life less stressful.
I killed it when I realized there was nothing left for me to do with it.
I connected with a lot of really smart and supportive people.
Didn't raise money at all, which gave me more freedom to turn it off when it wasn't working.
What I Think I Learned
I am an incurable entrepreneur.
People are willing to help if you ask.
I appreciate people who are willing to try something (anything) new. I try to acknowledge, congratulate, and encourage any effort to start something up now.
I learned that productivity software as a category can be radioactive to many investors . :)
I learned that every venture is a mix of successes and failures.