When God calls His child to live the life of a missionary, He gives him the desire with the calling. 
God has called every Christian to international missions, but He does not want everyone to go. God calls some to be senders. 
If someone does not have a missions heart at home, nothing magical happens when they buckle the seat belt on the airplane. 
God will not lead you where He will not provide for you. 
Hearing the missionary call has a great deal to do with what you are listening for. 