Two important things pointed out here are if customer is happy then the project can be said to be a success (what level of success ... it depends) and the attitude we bring in to to our work. People with a postive and "go get it " attitude get to do interesting projects but i have seen such people overloaded with work too.

There are many factors beyond our control which lead to failures. One thing i have found is the desire to use technology that people are most comfortable working with irrespective of the fact that it may not be the best option.

Another related thing is fear of failure due to which people dont want to try out new things/technologies.

Personally if you have been a part of a failed projects it all comes down how you managed the failure .