If the biggest mistake in sports is to dwell on the past, the second biggest is to pretend it never happened.

This should remind you that your Dallas Cowboys begin another long march today in Cleveland against the Browns. How long a march? Unlike the college game, the National Football League has a real playoff system, so that answer is to be determined.

Let's just say it would be pretty tough to justify a season that didn't last at least one game, probably two, longer than the previous two campaigns.

The Cowboys are a trendy Super Bowl pick, but tamp down those expectations for now. A spot in the NFC Championship Game would be a noteworthy accomplishment for a team that hasn't won so much as a playoff game since 1996.

That's six post-season defeats in succession, the last two particularly distressing. Two years ago, in Bill Parcells' last game as coach, Tony Romo fumbled the snap on a field goal that would have spelled victory in Seattle. Last season, in Wade Phillips' first playoff game as Cowboys coach ... well, we're not quite sure what happened, other than the Cowboys stumbling badly against a New York Giants team they handled twice in the regular season.

That those Giants ultimately upset the New England Patriots in Super Bowl XLII only adds to the misery.

The Cowboys return substantially the same cast, led by a flock of Pro Bowl performers that won 12 of 13 regular-season games before a lousy finish and then the playoff debacle. They are bolstered by some impact newcomers, including hold-your-breath cornerback Adam Jones. They open the season with no significant weaknesses, other than depth concerns at wide receiver.

And all of that will mean little if they can't get over the playoff hump in their final season at Texas Stadium. Those around the team with a sense of history should ask whether they want to be remembered like the can't-win-the-big-one Cowboys of the 1960s.

At this point, we'd be pleased if the Cowboys could just get to a big one.

As we said, no need to dwell on the past. But let's not ignore the lessons learned along the way.