overconfidence

From over- +‎ confidence.

overconfidence (usually uncountable, plural overconfidences)

1. An excessive or unwarranted degree of confidence.
   • 1890 February, A[rthur] Conan Doyle, “Sherlock Holmes Gives a Demonstration”, in The Sign of Four (Standard Library), London: Spencer Blackett […], →OCLC, page 89:

     My case is, as I have told you, almost complete; but we must not err on the side of over-confidence.

• overconfident