There are four forces that shape a project: site, user, material, and the designer.
The site is a dictator. It exerts more force over the project than any other. The site is both the physical and conceptual. The physical is geology, geography, hydrology, climate, and all the other natural forces; it is the infrastructure, the roads, bridges, utilities, water supply, and the other man-made aspects of the site. The conceptual aspects of the site are the social, cultural, and political forces that shape the site. These are such things as property definition (boundaries), zoning, codes, neighborhood identity, history, ethnicity, class, wealth/poverty, language.
The user is represented by the program – for what is the project to be used? How are the needs of the user to be accommodated? These needs manifest in distinct spatial requirements for different kinds of uses, and all of this has to be organized in specific relationships.
Material gives the project form. Material has to deal with the site forces: gravity, earthquakes, water, temperature, fire safety, but also has to contend with the kind of meaning that we ascribe to materials. Materials are part of the vocabulary of the language of design. Marble says something different than wood; oak says something different than knotty pine.
Finally, there is the designer. The designer is the mediator of the other forces, interpreting the interplay, and ascribing values and priorities.