他发现戒烟很难用英语怎么说

"Quitting smoking is difficult" 可以用英语表达为 "Giving up smoking is hard". 这是一个常用的英语表达，来源于人们在戒烟过程中面临的困难。

例句：

"I've tried to quit smoking multiple times, but it's always been so hard."
(我试过很多次戒烟，但总是很难。)
"Giving up smoking is one of the hardest things I've ever done."
(戒烟是我做过的最难的事之一。)
"Quitting smoking is not easy, but it's worth it for your health."
(戒烟并不容易，但为了健康值得一试。)