The presence of means and instruments is ordinarily associated with the occurrence of an act, but it does not follow that these things possess productive efficacy independent of God.
A customary condition accompanies an outcome in the normal order of events. Combustion in the presence of fire, or performance through a suitable instrument, can illustrate this relation. An exception to a customary pattern is not necessarily a logical contradiction.
Healthy faculties and usable instruments matter to human performance; they should not automatically be equated with the specific power concurrent with the act.