Scientists tell us that people who deny climate change, Covid-19, or other inconvenient facts are irrational because they are violating a fundamental scientific principle called the "Requirement of Total Evidence." In determining how reasonable it is to believe something, as well as act on it, you must take into account all the evidence available. You must not cherry-pick your evidence to suit your needs. Professor of Philosophy Peter Achinstein challenges this principle, considering scientific cases, a legal one, and an everyday example in which disregarding evidence is perfectly proper and the right thing to do. Visit www.jhu.edu/hopkinsathome for more lectures and mini-courses.