however strong you are, there is always someone stronger (idiom) / there is always sth more to learn / never be satisfied to rest on your laurels / there is no room for complacency
hand / (formal) to hold / person engaged in certain types of work / person skilled in certain types of work / personal(ly) / convenient / classifier for skill / CL:雙|双[shuang1],隻|只[zhi1]