ないと

ないと is a casual contraction used after the negative form of a verb to express obligation or a necessary action. It can mean "you must do ~" (as in ないといけない / なければならない) or convey a consequence if you don’t do it (e.g., you’ll be in trouble). It’s common in everyday speech among friends and family and is less suitable for formal situations. The verb stays in its ない form before と (e.g., 行かないと, 宿題を終わらないと). It can also appear after adjectives in the same sense (e.g., 忙しくないと間に合わない is less common; more typical usage is with verb forms). Generally used to state a necessary action or warn of consequences if not done.