פירוש על קידושין 120:14

The Mishnah rules that if he says “on condition that I possess two hundred zuz” she is betrothed only if he does possess it. But how can we ever be sure that someone does not own two hundred zuz? Maybe he does and we, or even he, does not know about it.
The answer is that if we do not know that he has 200 zuz, she is only doubtfully betrothed. If we know that he has 200 zuz, she is certainly betrothed.