A major reason for the failure of most missionaries is that the normal problems in Sunday church are packed into a seven-day week. Another problem involves jealousy and envy.
The translators of the King James version got this one right, while most modern translations got it wrong. "Jealousy" refers to a person having something, but being afraid that someone else will take it away. King Saul was jealous of David, fearing that David would steal his kingdom. Jealousy is not a big deal in the Bible, however.
"Envy" refers to a person who does not have something, but he feels that it should rightfully be his. The Bible talks a lot about the problem of envy, when a person demands a position, an honor, or leadership that someone else has. We'll see how this relates to missionaries.