Anyway, Alex was too stubborn to give up and it was like talking to a brick wall.

stubborn 是形容词，意思是"固执的、倔强的"，形容一个人不愿意改变自己的想法或行为，即使面对反对或困难也坚持己见。这个词常带有负面含义，暗示不合理的固执。