The investigations of some common misconceptions and false beliefs in police work and criminal psychology distinguish two types of false beliefs: those that are held despite research that indicates they are wrong and beliefs that might be valid but have not been subjected to scientific research. One proposal for preventing the adoption of misconceptions and false beliefs that underlie significant resource investments by police agencies and criminal psychologists is to find the original source for the belief or conception at issue. If there is no primary source based in scientific research, then the belief or conception must be viewed as unproven and unworthy of a resource investment other than for its scientific testing. The second principle for avoiding misconceptions and false beliefs is to only compare “apples with apples.” This means ensuring that statistics are correctly applied to the correct comparison group; e.g., comparing the suicide rate of law enforcement personnel with the general population violates the principle of comparing “apples with apples,“ since police officers do not reflect the broad diversity of the general population. Suicide rates for police officers should only be compared with those of a matched sample of the general population. The two other principles discussed are “Things are always more complicated than they seem” and “People are clueless.” The first principle means that policymakers and managers should be suspicious of simple answers to problems, and the second principle is to avoid basing significant resource investments on the opinions of supposed experts, absent objective analysis of all options. 2 tables, 4 notes, and 34 references