God appeared to Moses in a burning bush. A BURNING BUSH! What an obvious sign that God was about to speak something important! I know the task at hand, to bring the people out of Egypt, was not an easy one. I guess that's why Moses brought up every excuse in the book of why he couldn't do it.
There's a difference between knowing you're inadequate and that you need to rely on God, and whining, complaining, and making excuses with an "I can't" attitude.