Why do I lose money when I convert on Binance?

I'm quite confused. Whenever I convert my cryptocurrencies on Binance, I seem to lose money. Could you please explain why this happens? I've noticed that the conversion rate isn't always in my favor, and I'm starting to wonder if there's something I'm missing. Is it the fees? The spread? Or is it something else entirely? I'd really appreciate it if you could break it down for me and help me understand the reasons behind these losses. Thank you!