Of course, nothing can guarantee that similar reversals will not happen again in our lives in some way or another as long as we are still in the material world. As Srila Prabhupada put it: "a devotee is always pessimistic about the material world, but he is very optimistic about spiritual life." Of course, this does not mean that we have to feel depressed or that we should always expect the worst. This means, however, that we should not believe that we can find the kind of happiness that will satisfy the soul completely anywhere in the material world and its concomitant relations. As Srimad-Bhagavatam (1.5.18) says, one should aspire only for the kind of happiness that cannot be found anywhere in this material world, while expecting material happiness and misery to come on their own accord.
Collected Letters to Friends and disciples Vol 5, Pg 23, last paragraph.