There are two kinds of false confidence: the kind you believe to be true and the kind you don't. Both can cause trouble when you can't deliver, but when false confidence is expressed in good faith it's hard to really lay too much blame on the person in the short term; it was simply a mistake. If failure acts as a "market correction" and the person amends their behavior in such a way that they improve (always in many small increments, never in one swift move of grandeur) and subsequently gains a new high confidence that's backed by something real, the failure was a good and worthwhile one.
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I'd like to add to this too:
There are two kinds of false confidence: the kind you believe to be true and the kind you don't. Both can cause trouble when you can't deliver, but when false confidence is expressed in good faith it's hard to really lay too much blame on the person in the short term; it was simply a mistake. If failure acts as a "market correction" and the person amends their behavior in such a way that they improve (always in many small increments, never in one swift move of grandeur) and subsequently gains a new high confidence that's backed by something real, the failure was a good and worthwhile one.