只有 (zhǐ yǒu) is a conjunction meaning 'only if, only when' — it introduces the one condition that must be met for a result to happen, and always pairs with 才 in the second clause. It is stronger and more exclusive than 只是 (zhǐ shì 'merely, just'), which states a fact without setting a condition; 除非 (chú fēi 'unless') is the opposite perspective, focusing on the exception that would prevent the result.