naive

inexperienced or too trusting

Root

nasc / nat: born, birth, native, natural, or coming into being

Other words with the nasc / nat root

innate: inborn or built in
nascent: just beginning or coming into being
native: born in or belonging naturally to a place
natural: belonging to nature or present without being forced

Naive began near natural or native simplicity; now it means experience has not yet taught caution.

His naive plan assumed every form would be approved the same day.

The useful image is untrained openness. Naive can describe a person, plan, or assumption that meets the world before enough experience has added guardrails.