People often misunderstand the chance of 99%. Its 99% chance to be victorious but still 1% of defeat.
Meaning that in 100 fights you'll lose about 1 fight.
So in 100 missions you will fail 15 missions (if every mission has 85% success rate)
Simple math and i can't understand why some strange sci-fi or rocket science calculation has to be included for this. If its not 100% success, be prepared to fail!