sql tuning advisor suggested better plan does not work any better.

Recently i came across a situation that i used sql tuning advisor on a problematic sql and it suggested a plan with benefit 93%.I accepted the plan and ran the query which pick up the sql profile...but the sql performance actually worse than original one.

Then i gathered stats using estimate_percent auto and ran sql tuning advisor again.... it suggested a different plan again with benefit 93%.I accepted the plan and ran the query which pick up the sql profile...but the sql performance did not improve.

I have used sql tuning advisor for a long time but this was the first time i came across such a thing that plans suggested by advisor twice did not work....