In the nature of things: used for saying that sth that happens is normal in a particular situation and not at all surprising 理所当然,自然,丝毫不令人奇怪

Don't worry about it. It's in the nature of things for children to argue with their parents when they are teenagers.
青少年常常会和他们的父母争辩,这不足为奇.
In the nature of things, people who have power don't like losing it.
有权利的人不想失去他们的权利,这很自然.

let nature take its course:to allow events to happen without doing anything to change the results任其发展;听其自然

With minor ailments the best thing is often to let nature take its course.
对于小病,往往最好是听其自然.