Is there a concept in D&D where you can assume a 20 on a roll because you can retry as much as you want?

Question

I don't know why, but for a long time I though that a "natural 20" meant that a skill check was done under circumstances where the player can just retry an action until they get a 20, so the rolling becomes kind of pointless and you can just assume 20. For example, if a rogue is trying to pick a lock in an abandoned manor, they have all the time in the world and can just try and try until they succeed.

However I recently discovered that that's not what "natural 20" means. So... is there a concept like I described above in D&D and what is it called?

Answer 1

The rules for each edition of D&D are different, possibly including on this point. However, at least one edition of D&D did have this.

Taking 20 is an explicit option discussed in the rules of the “v.3.5 revised edition” of D&D.

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.

These rules appear in the section on skills, and skill checks in this edition have no special rules for a result of 20: if you get a 20, whether as a “natural” roll or by taking 20, all that means is that you can succeed at a task with a DC of 20 + your bonus.

Answer 2

This exists in 5e, but does not have a specific name

The 5e DMG has the following passage, under "Multiple Ability Checks" (page 237 - emphasis mine):

Sometimes a character fails an ability check and wants to try again. In some cases, a character is free to do so; the only real cost is the time it takes. With enough attempts and enough time, a character should eventually succeed at the task. To speed things up, assume that a character spending ten times the normal amount of time needed to complete a task automatically succeeds at that task. However, no amount of repeating the check allows a character to turn an impossible task into a successful one.

Thus, if a character has any chance of succeeding at a check, the DM estimates how long one check would take, multiplies that by ten, and declares the character to be successful after that amount of time. Since "any chance of success" implies that a character would succeed on a roll of 20N, this is essentially the "Take 20" mechanic from 3e/3.5e as described in KRyan's answer, but taking ten times as long as a regular check rather than twenty.

The 3.5e rules on "taking 10" and "taking 20" explicitly say that Take 10 and Take 20 cannot be done when a character is "threatened or distracted". The 5e DMG rule does not make this explicit, but it is implied in "the only real cost is the time it takes" (i.e., there is no cost of prolonged exposure to threat and distraction).

However, there are two important differences between the editions. First, while the 3e/3.5e rules explicitly say that you can "calculate your result as if you had rolled a 20", the 5e rules merely say that the character "succeeds", without making reference to a specific roll. The standard in 5e is for a successful skill check to simply be "successful", with no special consequence or outcome for a 20N. If there is an 'even better' success possible with a 20N (and see Does the degree of success or failure on a skill check matter?), however, then that would be triggered by a 3e/3.5e Taking 20, but not by the 5e procedure, since the 5e method doesn't assume a specific roll.

Second, the 3.5 rules assume that the character will fail before succeeding, and thus must apply any results of failure before the "Take 20" success is achieved. In 5e, in contrast, the unnamed equivalent may only be done, as previously mentioned, if there is no real cost to failure other than more time.