Tbh, I read that there were multiple Stasi Agents faking exactly that type of personality.
If you can't keep a secret besides that one important secret... Everyone will think you can't keep a secret.
... which means you couldn't be a spy.
Chunk: And this I've time, I mixed up a batch of fake barf, snuck up to the balcony at the theater, and made a noise like "huuuuh, huuuuh" and dumped it over the side.
Fratelli: I think I'm beginning to like this kid, ma.