What counts as a real theme in thematic analysis?

[Jack.G]

I'm analyzing interview transcripts for my master's thesis in sociology, and my supervisor suggested I use thematic analysis. I've read the foundational papers on thematic analysis social science research, but the actual process of moving from codes to themes feels really subjective and messy. How do you know when you've identified a genuine theme versus just grouping together a few similar comments? Is there a point where you step back and validate your themes, or is it mostly an iterative, intuitive process?