GMMichael
Guide of Modos
Guessing you meant "social skill checks" above, because "I want to use my skill to hop over the fence," isn't usually followed by, "okay, you think you hopped over the fence." Except, that's not what most skill checks do (that I've seen, anyway). A skill check, in D&D, is a success/failure determination, with an outcome determined by the DM.skill checks tell the character what they THINK is true.
Something like combat is more concrete. If you beat this AC check…you get to cause a quantifiable outcome of X damage.
Is there a concrete outcome to a skill check?
It's important to note at this point that since D&D lets the PC attempt anything, any listing of what's possible in skill descriptions will be incomplete. 6e seems to have made a concerted effort to change that with its tidal wave of new rules and codifications, but I think it still left a backdoor open with "you can improvise other actions."
So, the "concrete" outcomes you're looking for must be spelled out in the skill descriptions, don't cover all possibilities, and are limited to the other game rules with which they interact. Like the attack roll. "If you succeed, you deal damage." You're welcome to call those your non-terrible rules, but they don't define a very fun RPG. In that case, either everything is technically laid out in a massive set of rules, or you're constrained to a relatively small set of non-terrible rules. "Can I knock the giant's healing potion off its belt?" Must be answered by: "hang on, let's look up the Disarming Rules and see if we're allowed to treat it as a weapon," or "sorry, we got rid of the terrible rules, and that's not covered by the concrete rules."
So here we are; gray area, GM-fiat rules are necessary in D&D (but not all games). Some GMs and PCs are fine with rulings that affect PC free will. Others aren't. As far as I know, there's no D&D rule that says, "the DM can't make decisions for PCs," which is effectively what a successful social skill check does. It's also what Fear and Charm effects do. So I'd say that WotC supports the DM telling a PC that she "believes" something. For the OP, it's only a "waste of a skill" if you're telling it to the type of player who is out to win instead of play.