英语语法分析

A fiery steed is not trained in a courtyard, nor does a pine grow sturdy in a greenhouse.

院子里练不出千里马，温室里长不出万年松。

《新英汉大辞典》

Poseidon’s Steed: The Story of Seahorses, from Myth to Reality. By Helen Scales.

海神波塞冬的战马：海马的故事，从神话到现实

And this is very basic and involved part of man, so you should try to control this steed and keep him in check, something like this.

而这是人本性的基本而复杂的部分，因此你应当控制这匹马，将其掌控住，类似于这个。