The make-up of separate flights cost me 420 euros: when NOT convenient

To save money I bought Milan–Madrid and Madrid–Lima with two separate tickets and three hours between flights. The first started with almost two hours late, I had to recover my luggage and the second carrier did not repeat me. Between new ticket and night unexpected I spent much more than the unique flight. I would like to create a simple rule to understand when self-transfer is a reasonable risk and when price low is just an illusion. I am interested in a comparison based on recent experiences: indicated travel p…