Im not sure if anybody ever asked why Obito such a clumsy kid was teamed up with the 4th...Kakashi a kid who became jounin at 13, the 4th simpley a legend and rin a medical ninja at such a young age. What does Obito have thats so special?
Lets go back to when Kakashi was young... His group consisted of the 4th/Rin and Obito, now think why would Obito a clumsy kid be in a team with such great shinobi...
This takes us to the same basis of Team Kakashi nowadays with naruto who could relate to obito due to his clumsyness, sasuke with kakashi and sakura with rin. Obito has without a doubt some dark history or secret we havent been told about. Kakashi's Sharingan is differant then Itachi's, now it is highly possible that the sharingan Obito gave to Kakashi was a more purer version of the Sharingan, because as we all know those who possess the sharingan are extremly rare later on possibly due to the demonblood in the Uchiha becoming less and less with the newer generations. Obito's bloodline could have been the purest since Madara's. But something is still missing.
Care to add any ideas or prove me wrong? =)