For me, it was seeing that what was offered (by rightwing parties) was not relevant to where I was at the time as a student. I had no money, no job, no connections and no clue about where I wanted to go with my life. But I did know I didn't want to work in London, wearing formal office attire and being a slave to the nine-to-five grind for the rest of my days. The leftwing parties seemed to offer more inclusion and be more welcoming to ordinary folk like me. So that's where I looked for my political home.
Evidence suggests that watching debates has no impact on opinions whatsoever. A study tracking 100,000 respondents found no evidence that debates helped voters make up their minds.