ok but you can't ignore the fact that someone could have no knowledge of a certain subject, for me i have no idea on how to sail yet you expect me to have some basic? like what, *Point* ITS A SAIL.
Ah, another thing. Having a [-1]Mediocre Sailing talent is implying that you know what a sail and a boat are, and though you've probably never done it before, and would almost certainly fumble it a lot (and maybe even capsize!) you could figure it out given enough time and effort.
A skill at [-4]Abysmal is like my personal skill at Teleporting... EG. it is impossible. Due to the way the mechanics work, a skill at [-4] will, at best, only just barely succeed 1 out of 23,000 times. I don't know how that compares to Quantum Theory, but I don't imagine I'll be Teleporting any time soon. You'd have much better odds of fumbling your way through paddling a canoe or sailing a skiff, I imagine, even if it is a mission fraught with failure, and Titanic Reenactments.
... Q2. Would a person who is very proficient in mathematics have an advantage in mechanics tasks? I can't think of any other hypothetical situations here. Uh... Would a person with good woodworking be better at construction involving wood?
Some Challenges will let you flub skills... for example, building a lean-to shelter could use Survival Knowledge, Woodcrafting, or Construction. Art (Interpretive Dance) or Fortitude wont, however. BTW, when you perform a skill, you don't choose what skill to use first. You just describe what you want you do, and the dice roll from there.