This Thai idiom, naam lod taw pud (น้ำลดตอผุด) literally means, "when the water recedes, stumps emerge."
It paints a picture of a river -- any kind of body of water -- at high tide when all you see is the surface of the water. You have no idea -- nor do you pay attention to -- what lurks beneath.
Alas, what goes up must come down. Soon the water recedes, exposing things which have previously been submerged. What appeared to be in order is now chaotic, messy, ... embarrassing.
This scenario is akin to how in good times, with everything in your life going your way, all your flaws, hidden misdeeds, etc., are well concealed. And all people see is how great things are going for you.
In bad times, when all the props and crutches in your life get stripped away, things that have been hidden start to emerge -- like dead tree stumps underneath the water surface at hide tide. The chaos, the flaws, the scandals have always been there; they were simply concealed under the water.