I also would prefer to be able to interfere on failed rolls where appropriate, like when trying to save Arebella. You are suddenly faced with this really tough Die Roll to save her (18 iirc?!) and failure is flat out she gets killed. All along I was given the option to attack, let me keep it right up to the last second. Sometimes it doesn't work, I appreciate that, for story telling reasons or whatever, but in this particular example, if I failed to talk Kagha down and I see this going south, give me a last chance to interfere at my own risk. I might even go so far as to suggest a timer on the decision, but I like that stress aspect, others don't.
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So I tested this because I thought your estimate was super high for a DC on that as in 40+ playthroughs I have failed maybe a handful of times.
I realized you must have confronted Kharga as a Tiefling which gives you a -6 to the roll, or a DC 15 assuming no charisma or persuasion modifier.
However, if you then choose "1. Your snake is prepared to kill this child..." Kharga lets Arabella go without a roll.
So really the problem is you are dealing with Racism and you have no Charisma or skill in talking to people.
Alternatively you could chug a potion of Animal Speaking or cast speak with animals on yourself and talk to Teela, the snake, directly.
