When i wrote my first data structure (linked list) in c.
When I first learnt and used the concept of subqueries.
And way before that when i made a static website teaching c and made JavaScript output the result of c code i was explaining.
Also in my first job when i was debugging a shitty 2k plus lines stored procedure for days to realize that it was giving a wrong output just because a single variable was unassigned (null)