There are always different reasons why people do the things that they do. There are some who will do it because they want to improve themselves. They want to make sure that they will become best for the job that they are applying for.
There are also some people who would like to study and do things in order to learn something new and to become the best version of themselves. Some people also have high standards so they want to be able to live up to their very own standards. Of course, there are also some people who do it because they want to gain the approval of other people but this is not a part of Murray’s definition of achievement motivation.