To trust too much. Excessive confidence.

Is Overtrust a real word?

noun. Excessive trust; overconfidence, presumption.

What does the phrase trust mean?

1 : firm belief in the character, strength, or truth of someone or something He placed his trust in me. 2 : a person or thing in which confidence is placed. 3 : confident hope I waited in trust of their return. 4 : a property interest held by one person or organization (as a bank) for the benefit of another.