Observation in the field will tell you that it's extremely rare for a Westerner to spend more than 8 years in a developing country context without becoming bitter. If you want to avoid burning out, spend less than 8 years in the field before you return home (or somewhere like home). Don't even think about moving back for some years after that - even though you may still work in the same area and even pay visits (not too extended).
Your mental health is precious - don't expose yourself unnecessarily to risks of posttraumatic stress disorderW (PTSD).
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