"Do your best. Then, don't worry, be happy" Meher Baba
In a recent NY Times article, worry was reported to be beneficial. Those who worried about an outcome tended to have a less stressful reaction when the worrisome outcome occurred and a greater positive response when things worked out well. Those who did not worry, tended to be devastated when their optimism was proven to be unfounded and just mildly satisfied when things worked out as expected.
On the other side of the issue is the attitude expressed by the Rudolf Abel character in "Bridge of Spies" who when asked "Aren't you worried?" in reference to being convicted and sentenced to death for being a Soviet spy, responds coolly "Would it help?".