I was 21yo. I am thankful mandatory internships taught me that much.

1st internship at 20yo. Completed 2 full-fledged programming projects in 8 weeks, while I was supposed to complete 1 project in the entire 10 weeks. Spent the last 2 weeks unboxing and reboxing hundreds of products all day. Was paid 500€/month (minimum legally required). Worked my ass off from 8am until 18am. No one ever invited me to go for lunch with them. Boss treated me like an idiot. He once shouted at me at 8am because he didn't like my handshake and I didn't smile, I didn't look motivated and grateful enough to his liking.

2nd internship. 4 months long. Still paid the 500€/month minimum. Did my job alright, completed the tasks that were given to me and nothing more. Spent most of every Fridays just chatting with coworkers and drinking coffee. "Oh, it's 15:55 already! I better pack my things and leave". They loved me, told me they will have a position for me after I finish my studies. Colleagues offered me presents on my last day.

3rd and last internship. Applied the same principles. They offered me a job starting at 54k€/year (as a reference, other offers I got at the time maxed at 34k€/year).

I am thankful for this lesson. Be nice and socialize. Just do your job well with the time your are paid for and absolutely nothing extra. I have been nothing but successful in my career so far :)

P.S: all internships were in different companies