Originally posted by: SideLabel
I've been doing some thinking about this, and I've come up with some conclusions.
I would assume that, with time and training, a ninja learns and understands more about the theory of ninja techniques. So far we don't really know these theoretics. So after a ninja understand how a fire technique works he can practice on it to shorten the time he needs to prepare it, the amount of chakara he needs to use, and so forth. I would also believe that the more one understands jutsu and how it all works the more resistant one becomes. Take muscles for example. While working out one tears the muscle fibers in your muscles, and when they heal that is when they become stronger. It will take more effort to tear them again. The same could be applied to ninja techniques. After a certain time of using them basic techniques can be performed without though, while techniques that are more difficult require more effort and concentration.
But what makes a jutsu more difficult or hard to performe. Again this would fall into theory. So far we don't know WHY certain jutsu's are harder to perform than others. I belive that it has to do with the amount of chakara used, and what you are trying to do with it. A small amount of chakra sent out as a burst of flame would be relatively easy. A large amount of chakra sent out in the form of a water dragon, for example, would be harder because you are not only depending on other elements outside your control (water), but also the chakra has to be distributed far away from you and be given a distinct shape.
When people, such as Oro, says that "such a low level jutsu could never beat me", it is because they most likely know how that jutsu work, and are able to counter it's effects. If you know how to solve a math problem then it is no longer a problem, because you know how to solve it. See my point? Of course, this is all based on the assumption that there is a universal theory and law that applies for perfoming jutsu. Like the laws of physics, but only for ninja techniques.