The supply of financial need. Missionary ministries are more expensive to maintain than those at home. The problems of money exchange, export of currency, inflation, endemic bribery, etc., are constant points of concern. Adequate preparation for missionary work. Theological training, ministry experience, language learning, and adaptation to a new land may take years.
Culture shock is the subject of much humour, but is very real.
Many prospective missionaries cannot make the adjustment to new foods, life styles, languages, value systems, and attitudes. Balance and objectivity are needed. Protection from Satan's attacks. In many areas Satan's kingdom has never been challenged before. Missionaries need discernment and authority to resist attacks he makes through health, the mind, opponents of the Gospel, and even well-meaning Christian workers.