In my case it's not wanting zero failure, it's more a case of either my PC has the skills or she doesn't. When she kinda sorta has the skills but they're only 20-25% of the equation (at least at this point) and a dice-roll does the rest then I don't see the point of investing in skills. But as I said I don't come from a D&D background and I'm likely to be missing the point.
Its more that your charisma modifier reduces the requirement number so you have a higher chance to pass a skill check, i.e. you have access to more combinations if your requirement is lower. Its just that it does not have that much impact right now because a 2 modifier will reduce the requirement from 10 to 8, so you still have plenty of chance to fail. But the higher you have it, the lower the requirement will drop.
I think in D&D the correct way would be to add the modifier to the dice roll rather than subtract it from the requirement.
