let a thing slide
let nature take its course
In accordance with its natural tendency
順其自然,隨遇而安
〖諺語〗Don't trouble trouble until trouble troubles you
就順其自然吧。
"Well, I'll let nature take its course."
我毫無辦法處理，順其自然吧
I have no way to deal with it, let a thing slide
但是口語壹般說，let it be。