It all starts with a dream. Mary and Joe feel a calling to plant churches, and they contact a missionay organization. Or maybe they went on a mini mission somewhere, and liked it. That's when the process starts.
First, of course, it's required of them to go to bible school get a degree on missions, which looks great. But they are educated in theology, and not in missiology, even if the name of the degree is missiology. The problem is that bible school is all about information, and not much about practice. We learn how to understand the truths of the Bible, and we learn all the theory in evangelism and missions. But no practice.
After 3 or more years, Mary and Joe are ready for the great adventure. So they are sent to some place where a church has been planted for sometime by another missionary, but instead of doing missions, they'll be doing some kind of church ministry like they did in the church where they came from.
Finally, maybe after 1-2 years, they are sent to plant a new church. Normally, in a place where they don't know the language, they have no contacts (or maybe a couple of locals), and where they don't have a job (since they work full time for God). Not an easy task. And on top of that, they are really inexperienced in church planting, since they never saw anyone doing it, and neither helped in it.
This are the conditions a missionary meets when he gets somewhere to plant a church. No experience, no language skills, no job, no (or few) initial contacts. This is where it all really starts.
Preparation is of utmost importance. Bible school doesn't prepare you, real life does. And that's the first problem a missionary gets into. They really don't get the kind of preparation they really need. Bible schools and missionary organizations should provide an environment where missionaries could learn about missions in practice, not just in theory. That means working side by side with a seasoned church planter while he is planting a new church, not doing bible school for an already implanted church.