Kant’s parenthetical remark in the passage above is important.  For Kant, when one fails to will the necessary means to one’s ends, then reason has failed to have decisive influence.  In other words, one is irrationally incoherent.  Less guardedly, Kant says “the proposition (if I fully will the effect, then I will the action required of it) is analytic” (4:417).  But it is puzzling how this proposition could be analytic.  If it were analytic, then it would be conceptually impossible to be instrumentally incoherent since whenever one doesn’t will the means, then one doesn’t will the end.  (For a defense of this conceptual impossibility, see Finlay 2009.)  And if it’s conceptually impossible to be instrumentally incoherent, we’d be unable to make sense of why Kant formulates his account of instrumental incoherence in terms of imperatives, which, on Kant’s view, are commands addressed to a will that is capable of both following and not following the commands (Kant 4:414; Hill 1973, 430; Korsgaard 1997, 236).  So, perhaps we should read Kant’s claim as that if one wills the end, rationality requires that one will the means.  (For an alternative reading, see Lee 2018.)