[mothered]

The first "hack" I ever did was some SQLi.  

I believe this was the case with myself too (can't remember 25 years back).

Union-Based, Content-Based (Boolean) and of course Error-Based are very effective when applied and executed accordingly. Making the database wait for a response via Time-Based SQLi, can help determine whether the payload used Is true/false. It can be a time-consuming process, particularly on huge databases.