Skills you can take 20 on...

[cheshire_grin]

Sorry, but a skill roll doesn't have automatic failures, that is only for attack rolls and saving throws. If you have sufficient ranks in a particular skill, there is no way to fail it anymore, besides a DM that changes the standard DC for the attempt.

Then you don't need to take 20 at all; you just need a single attempt, no matter what you roll.

"Taking 20" does in fact assume that it is possible to fail the roll, and your character is merely going to try again until he rolls a 20. That's why you can't take 20 on skills that don't allow a retry.

If your ranks in a skill are such that you literally cannot fail the roll, then taking 20 would be stupid, as it's just going to make your success take 20 times longer than it otherwise would!

 

[irdeggman]

To add on to the above more detailed quote from SRD on Taking 20:

taking 20 is a different animal than a normal skill check - it assumes you will fail - which is why you can't take 20 on a skill that has penalties for failure.

Taking 20:When you have plenty of time (generally 2 minutes for a skill that can normally be checked in 1 round, one full-round action, or one standard action), you are faced with no threats or distractions, and the skill being attempted carries no penalties for failure, you can take 20. In other words, eventually you will get a 20 on 1d20 if you roll enough times. Instead of rolling 1d20 for the skill check, just calculate your result as if you had rolled a 20.

Taking 20 means you are trying until you get it right, and it assumes that you fail many times before succeeding. Taking 20 takes twenty times as long as making a single check would take.

Since taking 20 assumes that the character will fail many times before succeeding, if you did attempt to take 20 on a skill that carries penalties for failure, your character would automatically incur those penalties before he or she could complete the task. Common “take 20” skills include Escape Artist, Open Lock, and Search.