For Poirot, being a good detective means never getting carried away with an idea. Everything has to fit into a narrative that makes sense, but that doesn’t necessarily mean something that
seems obvious is true. To that end, Poirot recognizes that the substance that looked like salt in the cocoa might have been strychnine, but it
also might have been salt. Hastings, on the other hand, lets his excitement overwhelm him, and though it’s unclear whether or not the cocoa contained poison, it seems likely that Hastings’s unfounded confidence in this moment could potentially cause him to overlook other important pieces of evidence.