Jack Colby said:25% failure rate at low levels sounds fine to me.
It makes things interesting and unpredictable, which, from a game standpoint, is entertaining at the table. Give it a go, hero!
Here's the thing, DCs scale with level. So that 25% failure doesn't change, an epic character with epic skill challenges will have the same failure chance.
And for unpredictable, what I'm saying is when it comes to skill challenges its NOT unpredictable, in fact mathematically its quite predictable...your going to fail. If I take PCs and give them the least complex challenge of their level, they are still going to fail the vast vast majority of the time.
Let's say I put in a combat challenge into the game where I felt the players only had about a 20% chance of beating the monsters. That would be fine right....once in a while. Now imagine if I did that every single time. How would your players feel? Because that seems to be just how tough skill challenges are.
Alright, I'd done some more math. First off, my math was a little off in my first statement, and I must apologize for it. Instead of about 15%,
a 1st level party facing a standard complexity 1 level 1 skill challenge has an 18.75% chance of succeeding. That is still extremely low, and I believe my initial conclusions still stand, but its important to remedy my error.