Chance and the mean
Chance runs from impossible to certain; the mean is the total shared equally between all the values.
A worked example
The mean of 6, 10 and 14 is (6 + 10 + 14) ÷ 3 = 30 ÷ 3 = 10.
The mistake people actually make
Divide by how many values there are, not by the largest one. An outcome with no way of happening has a probability of zero.