easier said than done

It is easy to say that one can or will do something, but is much more difficult to actually do it.

说起来做某事容易，但其实做起来很难。

I know I should give up smoking, but easier said than done.

我知道应该戒烟，但说起来容易做起来难。

A: If you're not happy with yourself, then change.

如果你感到不开心，那就改变吧。

B: Easier said than done.

你说得容易。