Your first job will probably have a terrible shift. Finishing it teaches you that you can.

Your first bad shift is unpleasant and also the most useful day of the job. Until you have had one, you do not know whether you can be tired, blamed and swamped all at once and still see something through. Finishing it turns a worry about yourself into a fact, and that fact stays quietly available for years.

When a shift goes wrong, narrow it to the next task and then the one after. Do not negotiate with yourself about leaving halfway. Afterwards, notice that you finished, and tell somebody, because this is the sort of thing worth saying out loud once.