Definition
To be something that is extremely difficult to understand or explain; puzzling.
莫名其妙
It's one of life's great mysteries why some people can't quit smoking, even when they know it's bad for them.
為什麼有些人明知道吸煙有害健康卻無法戒菸，這是人生的一大謎團。
Why some people enjoy watching horror movies is one of life's great mysteries to me.
為什麼有些人喜歡看恐怖片，對我來說是人生的一大謎團。
It remains one of life's great mysteries why my potted plants always die, despite my best efforts.
為什麼我盡了最大努力，盆栽植物還是會死，這仍然是人生的一大謎團。