黄粱美梦
a fool's paradise : describes any situation that somebody thinks is good, without realising that it won't last---or that it's actually bad. 幻境,虚幻的乐境(短暂、不好)。
e.g. She is living in a fool's paradise!
她活在幻境中。
If you should lead her into a fool's paradise, as they say, it were a very gross kind of behaviour.