ST. ANDREWS, Scotland – There’s a touching scene at the end of the movie “Big” when Tom Hanks’ girlfriend realizes that he really is just a little kid who was magically made into an adult by a carnival machine called “Zoltar.” It was a lot to take in. “I tried to tell you,” he says. “I didn’t listen, I guess,” she says bewilderedly. “I didn’t hear you, or want to or how would I have … even if I did listen, why would I know? Why would I know that?” At this moment, I feel as disoriented as she did in that one. Until Sunday, I did not really believe Jordan Spieth could win the Grand Slam. Sure, the kid is impressive – more than impressive. Yes, he has the all-encompassing game that can win any week on any golf course. And absolutely, his composure is awe-inspiring both on the golf course and off it. Still, I just didn’t believe for a minute that anyone could really win golf’s Grand Slam. And now, after Sunday, I do. Now, let’s state the obvious first: Spieth is a long way from the Slam. Heck, he’s a long way from victory here at St. Andrews. He’s 12 under, a shot behind a couple of stars (Jason Day and Louis Oosthuizen) and an amateur who is actually eight months older than him (Paul Dunne). Three of the world’s top 11 players – Sergio Garcia, Justin Rose, Adam Scott – are just two shots behind Spieth. With the wind down Sunday, the Old Course was like a Chuck E. Cheese, with every player* having his very own birthday parties. Unless the wind howls (and it is not expected to blow exceptionally hard), Monday figures to be like that again. (* Except Dustin Johnson, who shot a miserable 75 that was more like an 80 considering the conditions and his length off the tee.) So, no, nothing is done yet. But Sunday, Jordan Spieth showed something. It isn’t entirely different from what he showed at Augusta when he won the Masters or Chambers Bay when he won the U.S. Open. But what he did Sunday on the Old Course with all the history on the line and doubts in the air, it sure seemed different. Look: Here was Spieth, winner of the first two major championships, on perhaps the world’s most famous golf course. And he wasn’t playing very well. Over a 27-hole stretch he was just even par, which is less-than-special this week. In the multi-day adventure that was his second round, he three-putted five times. Five! On the front nine on Sunday, he missed two good birdie chances and on the ninth hole he had a dreadful three-putt – one that prompted him to slug his golf bag in fury. “I couldn’t hold (the frustration) in,” he said. And he added, “I didn’t want to hit Michael (Greller, his caddie) so I figured I’d hit my golf bag.” At that moment, it was absolutely clear: The Slam had slipped away. That seemed bound to happen at some point. It always has seemed to me that winning all four major championships in the same year is impossible. Heck, what Tiger Woods did – winning four major championships in a row over two seasons – is almost impossible. But to do it all in a calendar year, to beat more than 100 of the world’s best players on four wildly different golf courses in a four-month span – with all the attention and focus on you and the ghosts of golfers shrieking in the background – well, that seems fully impossible. Nobody has ever done it. Palmer couldn’t do it. Nicklaus couldn’t do it. Player couldn’t do it. Woods couldn’t do it. See, golf is a game of the mind, and every crack of doubt, every sliver of uncertainty, every moment of hesitation weighs down the mind. When Spieth punched the golf bag, he was three shots out of the lead. It looked then that was as close as it might ever get. And then the kid birdied the 10th hole, the 11th hole and the 12th hole to move into the lead. That’s when it really hit home: This kid does not doubt. And this, I think, is the greatest gift in golf. I once asked Dan Jenkins what he thought separated Jack Nicklaus from all the other talented players, and he said this: “You can’t compare Jack with anyone else. It was almost as if he felt it was his birthright to win major championships.” Tiger Woods was like that too at his best. He didn’t have to fight doubt because he never felt doubt. And now, there’s Spieth. Maybe it’s because he’s 21 (he turns 22 next Monday) and simply hasn’t learned how to doubt. Maybe it’s because of his family, who so obviously raised him to believe without limits. Maybe it’s because he’s accomplished so much already. Or maybe he was just born with this unique talent. What is the first thing they tell you when you are trying to walk a tightrope? Don’t look down. But Spieth does look down, he looks down again and again. He knows exactly what’s on the line here. He understands it thoroughly. And he embraces just how high he is flying. Here’s what Tiger Woods said in 2002 when he was trying to win the third leg of the Slam. “I’ve got to play well and take care of business,” Woods said. And here’s what Jordan Spieth said:’ “I see it as something that’s only been done once before and it was a long time ago (Ben Hogan in 1953). That opportunity very rarely comes around. … And I’d like to have a chance to do something nobody has ever done. And so if I think about it that way, then I just want it a little bit more tomorrow, to be able to try and go into the last major and accomplish something that’s never been done in our sport. … I do recognize what’s at stake, and for me to accomplish that feat is going to be to simplify things and to just go about our business.” So, yes, Woods and Spieth ended their thoughts the same way, but Spieth was a little bit more expansive – he knows that he’s playing for the Grand Slam, and he knows what that would mean, and he knows enough about golf history to understand just how the odds stack against him. But you know what? He can do it. On the back nine Sunday, he played as if he had already won the tournament and was just acting it out for the public. To watch someone be that confident, that assured, that poised is inspiring. It’s at the heart of why I love professional golf. Jason Day could win on Monday. He’s an amazing player who keeps getting close and one of these days he will break through. Louis Oosthuizen could win on Monday. He already won an Open at St. Andrews five years ago and he understands how to do it. Padraig Harrington could win on Monday. He’s a three-time major champion who seems to have found his game again. Frankly, two dozen people could win the Open on Monday because the field is bunched up and the golf course is exposed and shootouts are unpredictable. But it sure seems to me that while a lot of players believe they can win the Open, Jordan Spieth believes he will. There’s a wide chasm between “can” and “will.” I believe, too.