Yes you have to think how everything interreacts, so it's a process of figuring out what your generally gonna need and keep going over the plan refining it till you have a solid plan and even after it's built you probably gonna have to refine it some more to dial it in how you exactly want it , I'm pretty sure he's just saying don't pick a random cam and try to make the rest of the car match it.
To me you first figure out where your not willing to compromise, like gearing, stall, cid etc.. then try to design for/around that. Example, If you must run 2.76:1 2,000 stall and like to keep NA 318 and want to do 11's something got to give, like NA and or cid and or 11's.