A traditional view of law and economics holds that an increase in the probability with which a court will convict an innocent defendant (type-1 error) lowers deterrence as much as an increase in the probability with which the court will acquit a guilty defendant (type-2 error). We demonstrate that this view is generally incorrect both when the court's error concerns the assessment of the act committed (mistake of act) and when it concerns the identity of the offender (mistake of identity). For mistake of act, the view ignores that adjudication involving a potential offender is generally less likely when he acts lawfully; there can e.g. then be no adjudication and hence no type-1 error when the sanction is harm-based and when the lawful act precludes harm. For mistake of identity, the potential offender may be falsely convicted of a crime committed by someone else whether or not he himself acts lawfully, and hence such type-1 error does not exert any direct effect on deterrence. Moreover, any indirect effect on deterrence is likely to be small because when the potential offender abides by the law, his risk of being subject to adjudication is generally shared with many other innocent people.