I don't know if it's just me but I found the modelling in mirror image of the illustration needlessly confusing.
It's ok, that's just at first, the more you do it, the less confusing. One thing with Blender is that there are so many ways to do the same thing, and there's no right or wrong, it may be more efficient or less efficient at times, but the goal is to get there in the end. Try watching a lesson again, it may grow on you the second time around.
I think you've both misunderstood. It has nothing to do with Blender and/or the mirror modifier. It's a comment on the content of the video.
In the video the illustration Jonathan uses as reference is often the mirror image of what he's modelling as he flips between referencing the left and right hand of the illustration while modelling the left hand of the model.
Oh that is nothing man, that is totally common and not an issue. One of the things I've heard people talk the most is then when you're starting from a concept art, you'd think everything is all set up perfect, but more often than not things wont line up, things will be missing, you'll only get one angle, the back side is not showing and you're going to have to use your imagination to complete it, etc. So using one hand to model the other, so many people wish that was all they had to worry about. So don't mind that at all, instead think of it as an opportunity to practice the harsh reality that is the big mess a production is.
Yeah I'm with Omar, focus on the finger, I doesn't really matter if its the right or left hand you reference from.
After all, the shapes of the fingers on the left hand are identical to the the index finger on the right hand.
If you are sculpting a human character and going for realism, then there maybe small detail differences, like a scar maybe, but the basic shapes are the same.
