Then they're not available when God does give them a job.
Debbie, missionary to the Ethiopians, told a ladies' Bible study I once attended that the sin of the people in the book of Jeremiah is that they didn't listen. It's everywhere in the book of Jeremiah once you start looking for it. Or, em, listening for it. God says to obey His voice, and walk in the ways He commanded them, that it would be well with them, "Yet they hearkened not unto me," the King James puts it. (Jeremiah 7:26) Sometimes it says, "They would not hear." (Jeremiah 13:11) And also, "You have not heard my words" or another translation actually says "you have not obeyed my words." Jeremiah 25:8.
If our hearts are in the right place, and God thinks we are ready, He wants to use us. He'll tell us what to do and when. In Ezekiel 22:30 God tells us, "And I sought for a man among them, that should make up the hedge, and stand in the gap before me for the land, that I should not destroy it: but I found none." He is speaking of the desolate and rebellious state of the land. God couldn't find anyone to stand in the gap for him. So many of us see that in our own land today and the cry of our heart is that we would be that person for Him.
We want to stand in the gap. Our hearts are right but we don't wait for His order. It would be like if our house was burning down, and the children wanted to help so they started organizing their stuffed animals or sweeping the floor.
You remember how king Saul got antsy and couldn't wait for God's order, but went ahead and acted on his own? He lost the kingdom after that. You know how Sarah knew God had told her she would birth a son to begin a great nation? But she couldn't wait for God to act and took it upon herself to go out and get Abraham to father a child through someone else. We're still feeling the sinful ripples of that lineage today.
We feel the urgency. That's good. Acting on it without God's direction, though, is not good. When we act on our own ideas or plans, we get the glory. When we act on God's ideas and plans, He makes it happen, He sees it through, He equips us. And He gets the glory.