In over (one’s) head: Too deeply involved in or with a difficult situation, beyond the point of being able to control or cope any longer.Having more difficulties than one can manage.(难题或麻烦，难度太大，某人难以驾驭)
Etymology: It is believed to have been first used sometime during the 1600s. As few average Europeans could swim during this period, being in water deeper than one’s head was to be in serious trouble.
中文释义：be in over one’s head 指某人处于明知不妙却又无法摆脱的地步,例句：Gaby, I am in over my head with this new job, and I need Lucy’s help. 其中over one’s head可指一个问题对某人来说太困难,如你在学校里学的一门课太复杂，很难懂，你就可以用这个习惯用语来表示。例句：That kind of math is just too far over my head. 在此引申另外两个习惯用语：out of one’s depth 超出某人的理解范围；茫然地，力不从心地（尤指不够熟练或缺乏经验）；Over the hump 是指某个人已经完成了一项任务当中最困难的部份，如渡过了一项工程、一个计划最困难的阶段，或者也可以说渡过了一个不幸处境的最紧要的关头。