There are people who make themselves available. They commit themselves to God's strategy and an assignment in it. Then, they feel it is up to them to make their assignment work. God is a general, and he commands, "Go. Take Philadelphia." So, the captain sits down, and conceives of numerous methods to conquer Philadelphia. And that's the last time he talks to the general. He does not know what the general will or will not support. He does not know how it ties into efforts in New York and Boston. So, if it fails, or does not succeed as well as he believed it would, he may wonder why there was not enough support, why supplies and replacements were slow in coming or why the general hung him out to dry.
Availability requires keeping in closer communication with God. It requires moment by moment dependence. Even if God gives a detailed twenty year plan, that does not there are not side trips and surprises. To walk in availability with God means we need to be willing to be interrupted.