My product/approach was too simplistic. It was just a word learner tool, basically a 'flash card' program, which tracked and modeled the user's knowledge, and 'annoyed' the user time to time with questions. My main mistake was that I did not research the market enough before building the tool: the problem exists, but there are too much competitors, and there a free ones amongst them.
Otherwise this was my smallest 'fail', because this did not involve that much work from me. My other 2 'fails' especially the first was a more severe one. (Google translate did not exist when I started my first project. I already had some paying customers when google translate had been made available in my language. Then I realized that I have no chance to keep up with them.)
