Don't bite off more than you can chew
Do not take over responsibility for a task which is too difficult for you to handle.
مسئولیت کاری را که بیش از حد برایت سخت است و نمی توانی از پس آن بر بیایی قبول نکن.
Julia, I don't believe you promised to finish the project before the summer. You knew it was impossible! Don't bite off more than you can chew.