What is the secret to cooking great sauces?

Cooking sauces is something I just don't know how to do. What's the secret? Why is it that on the cooking shows they easily throw in berries or something a little this and that and come up with something amazing that isn't gravy!?? (i.e., what's the secret here?)

Would love your suggestions.
Update: In response to one of the answers, how would you make a berry sauce so that it isn't too sweet, but that it isn't too watery, thick enough but not too thick, and possibly slightly indetectibly berry? You know what I mean? So that the sauce comes out awesome flavored but not pungent etc? Regarding a rue, it seems... show more In response to one of the answers, how would you make a berry sauce so that it isn't too sweet, but that it isn't too watery, thick enough but not too thick, and possibly slightly indetectibly berry? You know what I mean? So that the sauce comes out awesome flavored but not pungent etc?

Regarding a rue, it seems like gravy is gravy, it would be so neat to be able to cook some kinds of awesome sauces to tie in every dinner entree. Doesn't have to have flour or drippings. Could be other things. But what kind of sauces would be good?
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