What causes Indonesian to lenite word-final /k/, American English to lenite word-final /t/, and Spanish to lenite word-final /s/? This article shows that all three observed lenition patterns can be motivated using a single principle: languages preferentially lenite segments that provide relatively low informativity compared to the amount of informativity those segments carry in other languages. In a comparison of a diverse sample of seven languages from the LDC CALLHOME and CALLFRIEND corpora, Indonesian /k/, American English /t/, and Spanish /s/ are found to have the lowest informativity, predicting that they would be more likely to be affected by sound change processes. In a subsequent regression-based corpus study, low informativity predicted the propensity of word-final lenition of all obstruents in American English after phonetic and phonological factors were controlled for. This article therefore provides a partial solution to the famous actuation problem (Weinreich et al. 1968) with respect to the actuation of lenition processes.