Originally Posted by platinumrug
The reason why it took Naruto a shorter time to learn Rasengan is because it has no affinity attached to it, it's just pure chakra molded into a tight ball using shape manipulation. Hence the reason why he had to figure out his natural affinity so that he could apply it to his Rasengan.
Yes that's all true, however Rasengan has a much higher level of shape manipulation then Chidori so it kind of evens out. Besides sasuke already knew how to do elemental recompisition for his fire element so learning to do it for lighting shouldn't have been that hard. Plus he had sharingan to help speed up the learning process.
Not that it matters, but originally stubborn_naruto was trying to say Sasuke's primary element was lightning when anyone who's read the manga knows it fire. I was just pointing out if that were true then it wouldn't have took as long to learn chidori (it would have likely took 3 weeks instead of a full month), because he would already learned to use lightning recompisition and the shape manipulation for chidori isn't that hard.