About half of all cross-cultural missionaries return home early without completing their first term or don't return to the field after their first furlough. Here are the most common reasons why missionaries return early.
1. Sending church lowers or ends support
Churches in the West are aging and emptying. A quarter of them can no longer afford their own pastor. Many missionaries try to hang on financially until their first furlough, hoping to close the deficit then and line up enough support to return to the field, but end up staying home when it falls short. Ultimately, God keeps in the field those whom He has called and gives them their sustenance "daily" (Matthew 6:11), which is easier for single missionary men and single women missionaries than for married missionaries with children.
2. Failure to adapt cross-culturally
The missionaries sometimes, their spouses often, and their teenaged children increasingly lack the ability and/or the desire to learn and adapt to the local culture, language, climate, technology deficiencies, inefficiencies, hygiene, food, etc.
3. Health issues
Contaminated water and food cause food poisoning, parasitic worms and amoeba, while mosquito bites lead to dengue fever and malaria. Extreme air pollution causes respiratory illnesses, including in India and China, while stress and exhaustion weaken the immune system, trigger depression and other (latent) mental illnesses. The lack of Western healthcare can prompt (emergency) repatriation, including for children and after botched medical procedures by local doctors.
4. Unmet expectations
Inspired by biographies of missionaries who baptized masses, as well as exaggerated reports from current missionaries, many new missionaries arrive in the field with high expectations, then become disappointed and demoralized when the expected harvest doesn't materialize, while others come for adventure and deflate after the initial euphoria.
5. Conflict with colleagues
Cultural differences and misunderstandings, as well as jealousies, politics and power plays lead to tension, even clashes between missionaries, as well as between missionaries and the mission board and/or local partners or employees that remain unresolved and fester.
6. Exposed sexual sins
Single missionaries, both men and women, get lonely and seek companionship that leads to fornication, while married missionaries commit adultery, including with fawning members of the planted church.
7. Family formation or expansion
When single missionaries marry and have children, their priority shifts from the Lord's harvest to raising their children, which is easier back home with family support.
8. Inadequate schools for children
International schools are expensive and found only in major cities, while local schools are inadequate for preparing for US colleges, and missionaries could feel too busy to homeschool. Some return home intending to return to the field after their youngest leaves home for college but many never return, while those who do return have spent their most energetic years away from the field.
9. Rounded resumes
Recent graduates with newly-minted Master of Divinity degrees come to round out their resume and use it to land a pastorate back home.
10. Family obligation back home
Elderly parents lose independence and/or become sick and require care.
11. Deportation
Governments of countries hostile to the Gospel deport missionaries caught proselytizing, including to save face or to make a political statement.
12. War or terrorism
Mission boards have thresholds for pulling out missionaries when war or (Islamic) terrorists approach. A rare exception is Free Burma Rangers.