Alright. So let's do the math.
With no bonuses, you try to pick a DC10 Lock, you need to roll a 10 or higher. On a 20-sided die, that's exactly 50% chance.
If you add a plus one bonus, now you need to roll a 9 or higher to get a succes. So, add a one-in-twenty, or 5% increase to the odds, putting you at 55% cahnce.
With advantage, you're rolling two dice instead of one, picking the higher number.
You have 50% chance of rolling 10 or higher, twice - putting the odds that at least one of them goes to 10 or over, at 75%.
If you were to have disadvantage, however, tghat's the other way around. You roll two dice, but have to pick the lower result, and that, then, puts the odds for that same lock at 25%.
The highest chance with straight up modifiers you can have on a single Die roll is 95%, as a 1 always results in failure.
So, 5%, or one in twenty auto-fails.
But, with advantage, the odds of both rolls resulting in a 1, is 0.25% or 1 in 400.
So, with a +18 Bonus to a skill or attack, the odds of you succeeding with advantage is 99,75%
To illustrate with a real-in-game scenario.
There is a vault door somewhere. You can open it with a puzzle, or try to pick the lock. The lock's DC is 99. No amount of bonuses you accrue in this game puts you *that* high, but you can still manage that door by going for crits, or natural 20's.
Rolling a single die, that obviously, statistically, would cost you around 20 thieves tools before you get in there.
WIth Advantage, however- your odds are doubled - you now 10% chance at succeeding per roll. And it would probably cost you around 10 thieves tools before you pick the lock.
So, getting advantage on things *really, really* offsets the odds.
Last edited by rodeolifant; 04/09/23 10:04 AM.
