Retiring in Southeast Asia might be a lot harder than you think

I am a European guy, lived in Southeast Asia for over 10 years, worked and travelled a lot in Vietnam/Indonesia/Philippines/Thailand. Occasionally, a thread comes up where people discuss the naïve and romanticized idea to retire in one of these places on an Ultraleanfire budget. I have seen this idea go horribly wrong countless times. Mistakes to avoid when retiring to Southeast Asia.