Naivety is the noun for the state of being naive — the lack of experience that makes someone trust too easily and expect things to go well. You meet it most often in a small set of fixed shapes: with a possessive (his naivety, their naivety), after out of or with (out of sheer naivety, with the naivety of a child), and in phrases like a certain naivety or the naivety of youth. It is an uncountable noun most of the time, so you say a lot of naivety rather than "many naiveties". The tone is usually a mild, forgiving criticism: pointing at naivety says the person meant no harm but did not understand the situation. Writers and journalists like it for describing politicians or businesses that walked into an obvious trap. There are three spellings in use — naivety (most common in British English), naiveté and naïveté (the French forms, which look more formal or literary) — and all are considered correct. Sometimes people also say naiveness, but that is rare and you do not need it.