What is most important part of a system?

I remember reading someone saying that the most important part of a system was the source. I thought "Wrong! Speakers are the most important".
 
Now, I have changed my mind. Source is the most important part.

Right or wrong but this is how I came to this conclusion;

I have tried the same system with a CD player and a turntable. By far LP sounds better than a CD. Btw, the system had all high-end amps, speakers, cables, etc.

What is most important part of a system for you?