Software as a craft
I think that every application is a unique piece and the creation of software is more related with the craftmanship than any other industrial processes. From my point of view, creating an application have more to do with the creation of a film than the creation of a car, in the sense that every film has its own problems and its own solutions.
Users many times don't know what they want
A lot of times, people don't know what they want until you show it to them. Steve Jobs.
The vision of a single person, or a group of people about a particular subject is limited. Build something based in this vision can lead to disaster. It's better build a prototype and then work modifying this prototype as an iterative process than taking requisites and then build a complete solution based on this requisites.
Source code is the only updated document
Never ever in my life I've seen a source code that lies. Never ever in my life I've seen an updated analysis.
Keep it simple, stupid