Probability question: Advantage and Disadvantage

[OnlineDM]

If I'm understanding this correctly, in a battle with 2 goblins: a guard (AC12) and his chief (AC19), advantage against the guard gives me a +5 or so, whereas advantage against the chief only gives me a +2 effectively. It makes sense that the tougher opponent would be more difficult to hit, but there is a bit of a law of diminishing returns isn't there. What's the incentive to try to gain advantage against the tougher opponent?

I think I might think its a good mechanic, but maybe I'm missing it.

This is only true if your attack has +0 to hit. If you take the dwarf fighter from the playtest, he has +6 to hit with his Greataxe. This means he only needs to roll a 6 to hit the guard or a 13 to hit the chief. Having advantage when you need a 6 on the die is equivalent to just shy of a +4, and having advantage when you need a 13 on the die is equivalent to almost a +5.

It only has diminishing returns at the extremes - when you'll be hitting on a 2 or 3 on the die, or when you need an 18 or 19 on the die to hit, for instance. D&D rarely puts players in that situation.

 

[Rampaging Lawn Gnome]

Double post.

 

[mkill]

What's the incentive to try to gain advantage against the tougher opponent?

Because even if you need a 20 to hit, it's still better if you get two tries to do it.

However, if you need a 20 to hit an opponent, it's probably better to run.

 

[DNH]

What's the incentive to try to gain advantage against the tougher opponent?

Because even if you need a 20 to hit, it's still better if you get two tries to do it.

Precisely. All this talk about probabilities and averages but those averages are only valid over time; there is no average result of a single die roll - each result , 1 through 20, is equally probable. So having two throws of the dice is clearly desirable.

[And I really need to change my sig line.]