When dealing with data, a common assumption is that – data either proves or disproves something, straight up. There is no ambiguity. Or at least, that is what one usually assumes about data.
However, the truth is that where there is data, there is bound to be uncertainty. And visualizing uncertainty is an important part of visualizing data if one is to responsibly present data. This post does an excellent job of explaining the pros and cons of various ways of visualizing uncertainty in data.