After explaining that what he really fears is the Swiss, who now "have entered Lombardy with the excuse of putting the present duke back there, but in fact they themselves are the dukes," Machiavelli argues that from Lombardy they are almost certain to overrun all of Italy*, and that thus "one needs to be exceedingly afraid of them."
Knowing that Vettori would be reluctant to take this view, Machiavelli continues,
I know that to this opinion of mine is opposed a natural defect of man: first, wishing to live from day to day; second, not believing that anything can happen that has not happened; last, always reckoning about a person in the same way.About the first of these, it seems to me that we can--and maybe should--do little: despite being by nature a planner, I, too, like to live from day to day, and I think that temporary fixes deserve a better reputation than they generally carry. The latter two, however, are recurrent problems that I've never before seen described so succinctly. Put so well, the pitfalls Machiavelli describes seem eminently avoidable; would that that were the case.