I'd say that science is frustrating in that it can rarely say, "This is 100% true" in a way most people can understand. Something could come along and upset the apple cart. Gravity is a good example - it's pretty reliable in practice, but we don't exactly know how it works.

People want answers. But aside from the definitely gray areas of non-science, the natural world works in way that aren't comprehensible to the average person.