It's a given: Man ain't God.

That seemingly obvious thought occurred to me throughout a screening of the film Ali, to be released on Christmas Day.

Isn't it true that whenever a man is considered heroic, and ascends to great heights, he inevitably falls to earth? He is, after all, just a man.

Muhammad Ali, Martin Luther King, and, more recently, Jesse Jackson, all shouldered some heavy responsibility. King was the torchbearer for an entire race in the '50s and '60s. Jackson was the first black man to be a legitimate presidential candidate in the '80s. Both men were preachers on Sundays. When a man drinks from both a political and a spiritual cup, it's not hard to get drunk.

When I learned of King's infidelities and, much later, of Jackson's illegitimate child, I was surprised. Then it struck me that for them, as for Ali, the pressure to be great exposes fundamental human imperfection. And sometimes even causes it.

In Ali, that was captured in one scene. It takes place in Zaire -- site of Ali's fight against George Foreman. Tired of Africa, Ali's second wife, Kaliah, had flown home to Chicago. As Ali (Will Smith) speaks to a group of people, a young female reporter named Veronica sidles up to Ali and introduces herself.

The next few scenes contain very little dialogue; the camera follows Ali, arms linked with Veronica -- who would later become his third wife -- through the streets of Kinshasa. The fact that he's already married is, at most, an afterthought. It's a given that the Champ, a man larger than life, should accommodate every woman he can.

The scene reminded me of a modern champion, Evander Holyfield (who, sadly, is still fighting). We know Holyfield to be a very spiritual person. The man quotes scripture before and after every bout. He's also a man who has denied himself drugs and alcohol, but he still has one very visible worldly vice: women. Of his nine children, five were born out of wedlock -- two of those were fathered while he was still married to now ex-wife Janice.

Before and after every fight, Holyfield proclaimed himself a man of God. After the second of his three epic bouts with Riddick Bowe, Holyfield stood in the ring and said, "I walk by faith, not by sight." A Christian testimony by a man I think really is sincere in his beliefs -- but his chosen path winds so high above humanity that it has to be hard for him to breathe.

But a great fighter, a great athlete, or a great man, ain't God.

Ali shows us that. I like the way the film takes us through Ali's dramatic knockout over Foreman, but not past it. We all know what happens after that.

We know there are more women. And divorce. Ali loses, then regains his title. And of course there is the onset of Parkinson's disease, which leaves him a palsied, shaking shadow of his former athletic self. I'm glad we don't have to go through that with him on the big screen. We just know.

We know that after revolutionizing a sport and becoming an ambassador for peace, he ages, and is brought low, like a normal man.

He is great. No question. But he ain't God.

And that's a given, isn't it?

Alan Grant, a former NFL defensive back, writes football for ESPN The Magazine. E-mail him at alan.grant@espnmag.com.