My knowledge of actual functions was poor, but I already had myself as "ISFP" just by common sense and comparison with other people. Then I had strong experiences of ITR particularly supervision from LSE and quasi from ESI, identity from SEI and also duality from ILE. From then on it was just about learning more and getting a clearer picture.
The thing that blew my mind the most was that I realized I had actually experienced supervision from LSE many times before Socionics, I knew exactly what it felt like but discovering it again as a part of this system was incredible.
EDIT: My real type struggle happened back in my MBTI days. I wanted to type myself as an intuitive at first, then I wasn't sure, and I got obsessed. I examined all types and thought about people I knew and concluded that ISFP fits me best if I'm honest. Funny thing is that it wasn't until Socionics with all the additional facts and ITR that I could really know that types are real and be absolutely sure. But I had typed myself correctly back then and I am proud of it. It must have been INTUITION.