what are the factors that stopped mumbai indians before semis???

Main thing is Jayasuriya did not come into his form and if he did it would have made a huge difference even if the others play well or not. Then the story would have been different. Same with Sachin, he wasn't in form. Then team management was not very good and experiments were too much. Sometimes may be Sachin had flaws in his captaincy too even though he is a brilliant player. The changes were not done at the right time,Jayasuriya and Duminy should have got more chances with the ball.

I believe its lack of self confidence in crunch situations. Against Rajasthan Royals you cannot expect to lose 4 six wickets for 4 runs in the last over, when they needed only six.