The intricacies of game mechanics

Well, when checking for +morale, a random number from 0 to 23 must be less than the stack's morale for it to pass, and when checking for -morale, a random number from 0 to 11 must be less than the stack's -morale for it to trigger.

Example: morale +2, then there are 22 values in the unsatisfactory range (since only 0 and 1 are correct), morale -2, then there are 10 values in the unsatisfactory range. Hence, the probability of morale occurring is 2.2 times higher (although there seems to be a different opinion on this in probability theory).