I have a computer model, which I use for predicting the weather. The algorithm is fairly straightforward and goes something like this:
It will rain tomorrow.
(Round where I live that's likely to be a pretty effective prediction.)
Anyway, if I run my computer model repeatedly, I find that 100% of the runs give the same result - "It will rain tomorrow". I conclude, therefore, that we can say with 100% confidence that it will rain tomorrow.