Originally Posted by Wolverine
KYF... I guess Shisui could use Kotoamatsukami regularly, but for an outsider to use it as effectively, it would need a strong chakra source like that of a Senju (Hashirama being the strongest). That is why Danzo implanted it in his arm, because it might have made it easier for an outsider to use it just like an Uchiha...
That's my guess too. Shisui would have needed to use the ability several times before he actually learned the extent of it. Probably the time factor was not a major problem for him, but if the eye got transplated, the ten year span should have come in effect.