wimp out (of)
A:Could you give me some advice on how to bring up my son properly?
A：怎样才能教子有方，你能否给我提点建议?B:He's a bright boy, isn't he?
B：他不是很聪明吗?
A:But he always wimps out of difficulty.
A：可他总是一遇到困难就后退。B:Don't worry, he'll make good progress step by step.
B：别着急，他会慢慢长进的。