半斤八两much to choose between

班门弄斧show off one’s slight talent/skill before an expert

半途而废to give up halfway;to leave something unfinished

饱经沧桑having lived through many changes

杯弓蛇影be jittery;suffer from imaginary fears (lit. to see a bow reflected in a cup as a snake)

背井离乡be forced to leave one’s home (for a remote place)

本末倒置confusing cause and effect;to reverse the primary and secondary tasks (lit. to invert root and branch)

必不可少absolutely necessary

闭门思过shut oneself up and ponder one’s mistakes

变化无常irregular;capricious