Essentially what he is saying is that it is better to take initiative and do what you think needs to be done rather than try to get approval first.
There is a parallel here to startups -- no risk no reward. By taking on a project without approval you are basically putting your job on the line. If your manager approved the project, he would be on the line. Unless he really believes in the idea, it's unlikely he will do that. Better to wait and see how you do and then pile on once success seems more assured. You will find the same thing with investors -- noone wants to give you money until you are already successful.
There is a parallel here to startups -- no risk no reward. By taking on a project without approval you are basically putting your job on the line. If your manager approved the project, he would be on the line. Unless he really believes in the idea, it's unlikely he will do that. Better to wait and see how you do and then pile on once success seems more assured. You will find the same thing with investors -- noone wants to give you money until you are already successful.