Originally Posted by Seerow
This part, however is not. What you should and should not be able to do should be based on what the modifiers add up to allowing you to do, not based solely on what the DM thinks is acceptable. If you want the Rogue with 18 dex and balance trained (+7 modifier) to be able to succeed reliably, that check DC needs to be 17 or lower. That means your Wizard with 8 dex and no training (-1) can succeed on that check 15% of the time. Telling him he can't even roll to attempt it is robbing the player of that chance without any mechanical reason for it.
The situation I described should was meant to be something that even a very skilled, very dextrous rogue would have trouble with (+7 mod, minimum roll 10, automatic advantage), so a DC of at least 20, probably more along the lines of 25.
My point wasn't the specific situation, anyways, so if you don't think that fits, then just imagine an even more ludicrous situation that would call for a DC that high.