Ask the Lord to give your missionaries good contacts. They need to discover productive ways of reaching people in the culture where they are. Pray also that national believers will have an evangelistic zeal for their own people, and pray that there will be receptive hearts among those to whom the gospel is presented. In foreign countries just the daily stress of living can be daunting to the missionary. Unless one has lived in other cultures, this is difficult to understand.
Shopping can be quite a chore and require many hours of time.
In certain areas the climate can be stressful. Interactions with government officials can be exasperating and time-consuming. There can be interminable delays in securing needed goods or services. Satan is active and is opposing attempts to win converts and plant churches. Progress can be agonizingly slow.