💡 Detailed Explanation
The context 'couldn't grasp the main point at all' suggests a word that means unclear or open to multiple interpretations is needed. '曖昧' (aimai) refers to something that is not clear and can be interpreted in various ways. '漠然' (bakuzen) means vague or obscure, like an unfocused outline. '微妙' (bimyō) means subtle or delicate. '不明' (fumei) means unknown. '曖昧' is the best fit for an unclear explanation.