Why Yuvraj and Raina can't be great test batsmen?

Most people think once a player has succeeded in the 50 overs format it is quite an easy transition to the test format. If one looks closely it is not so easy. In test cricket one needs to stay at the crease to for a long time (with the great exception of Sehwag and Gilchrist) to have a substantial score. That means surviving the good balls and hitting the bad balls for boundaries. To survive one needs to have a good defensive technique i.e. good balance, head still, feet moving to the pitch of the ball, knowledge of location of off-stump and clarity of thought whether to leave the ball or play it.

Yuvraj has problems with the short ball but the more glaring problem is his lack of feet movement and balance against the swinging(or seaming) ball. Also outside offstump he is sometimes not quite sure whether to leave the delivery or play it. Also he is footwork against spin leaves a lot to be desired.

Raina is a compulsive hooker/puller of the short ball and often he is not in position when he plays those shots. Also as he is expecting a short ball barrage every time he can get stuck in his crease and the over-pitched swinging (or seaming) sucker ball can be his undoing. One advantage he has over Yuvraj is his footwork against spin which is quite sublime. But he has the tendency to slog over mid-wicket (his favourite shot in the shorter versions of the game) which can lead to his downfall.

When teams play test cricket they normally analyze every player in the opposition team and since in test cricket there is a lot of time they try to work on weaknesses of every player in the opposition. If one gets out in the same way a few times it becomes a mental aspect for him. So, while Yuvraj and Raina can succeed in test cricket it will be difficult for them to become great players with so many technical shortcomings.