That’s barely enough time to get the hang of the job! 

When you’re young, it’s very common to have stints of a couple of months on your resume. You’re probably not going to get rejected from working the front desk at your college’s gym because you only stayed at your previous job at Panda Express for five months. Entry-level service jobs with high turnover rates can’t really expect 18-year-olds to have years of consistent work experience. The 18-year-olds who do have such experience are probably looking for a gig a little more prestigious than their last one. 

Internships are one of those jobs that tend to last a summer or a semester, so they’re typically only 3-4 months at most. Depending on the intern’s tasks, that might be plenty of time. If their only job is to get the boss coffee and occasionally proofread a briefing, they’re going to get as much out of that in 3 months as they would in a year. 

Once you move into the working world as an adult, you learn that job hopping, moving from one job to the next every couple of months or years, it starts to become a red flag. Most full-time jobs are not designed for employees to constantly come and go. They expect hard work and growth over a period of years, with most employees not getting the full hang of their jobs until at least one year in. The employee in this story doesn’t get why 3 months is considered a «short» amount of time to stay at a job, and I can only assume he believes that because he’s never worked full-time.