Consonant lenition refers to a list of seemingly unrelated processes that are grouped together by their tendency to occur in similar environments (e.g. intervocalically) and under similar conditions (e.g. in faster speech). These processes typically include degemination, voicing, spirantization, approximantization, tapping, debuccalization, and deletion (Hock 1986). So, we might ask: What are the commonalities among all these processes and why do they happen? Different theories attribute lenition to assimilation (Smith 2008), effort-reduction (Kirchner 1998), phonetic undershoot (Bauer 2008), prosodic smoothing (Katz 2016), and low informativity (Cohen Priva 2017). We argue that it is worthwhile to focus on variable lenition (pre-phonologized processes) in conjunction with two phonetic characteristic of lenition: reduced duration and increased intensity. Using mediation analysis, we find causal asymmetries between the two, with reduced duration causally preceding increased intensity. These results are surprising as increased intensity (increased sonority) is often regarded as the defining property of lenition. The results not only simplify the assumptions associated with effort-reduction, prosodic smoothing, and low informativity, but they also are compatible with phonetic undershoot accounts.