gullibility

/ˌɡʌləˈbɪləti/
noun
  1. The quality of being easily tricked or fooled because you trust people too much.
    • His gullibility made him an easy target for online scammers.
    • The con artist took advantage of the elderly woman's gullibility.
    • She learned to be more skeptical after her gullibility cost her a lot of money.