Every good method is founded on some underlying principles that guide the decisions you make in implementing the method. They also guide the practices that the method espouses. Principles glue your practices together into a unified and coherent whole.
Failure is inherent to software development, and not exclusive to business intelligence solutions. Don't be afraid to try something with PowerPivot for Excel that would have been impossible with just Excel. For example, you can put far more data into PowerPivot for Excel than Excel alone could ever handle. I have loaded tens of millions of rows, on the same local network as the source database server, in a matter of minutes. For the vast majority of users, little you do ...