Behaving like a leader doesn't mean you will get to lead
On what leadership is, the interpretation that I'm most familiar with and resonate with is Seth Godin's, which defines all instances of "leader(s)" and "leadership" in this post. It is also implied that leaders strive to make universally positive changes. Using that definition, I believe that everyone can, and probably should, behave like a leader when the opportunity arises.
However, just because you are behaving like a leader doesn't mean you will get to lead: you may not be privy to some information that would let you plan better; others may view your leadership as a threat to their authority, status, or beliefs; and so on. Assuming you have already tried your best to negotiate those obstacles, the only thing left to do is to accept that the change you seek to make is not for them and move on (and maybe bring those who believe in the change you seek to make with you).
None of that is new but the stage is set now. More on what prompted this post tomorrow!
Edit: fixed typos and the title.