The impossible appeals to me. Self-possession, grace under pressure and generosity do, too. So, Mark McGwire's 70 home runs and Jack Nicklaus's victory at The Masters at the age of 46 are my favorite events I've ever covered. If forced to chose, I would pick the former. Because no one has ever "lost" better than Sammy Sosa.

Athletics, at its best, pushes at the very limits of human possibility. Doing what has never been done is remarkable. However, doing what has never even been realistically discussed is an entirely different animal. We feel ennobled by watching others do deeds--and act with a strength of character--that even they themselves assumed was probably beyond them. When those who are The Best Ever surpass themselves--and are left almost numb in their own presence--we stand taller, too.

No one, including Babe Ruth, ever hit home runs--so many and so far--like Big Mac. No one, including Bobby Jones, ever played golf so well and so long as the Golden Bear. Yet, once in their lives, they even went beyond their own parameters. Many athletes have said, "I can't believe I did it." But, perhaps, we've never believed any of them as deeply as we believed McGwire and Nicklaus, because we hadn't even imagined the possibility of what they actually did.

If hitting pitches over roofs and hitting balls into holes were the only issues, other events might compete with these two landmarks. But the residue of Nicklaus in the spring of '86 and both McGwire and Sosa in the fall of '98, seems, with time, to be more and more about their admirable qualities as people.

Their personalities rose to the moment as much as their muscles.

McGwire lifted his son the batboy over his head as he crossed home plate. That was the proper image to capture a man who spends his time and fame fighting child abuse, not glomming on to more TV ads. McGwire also stepped over the box seat railing to include Roger Maris's family in what might easily have been his moment. Instead of celebrating himself, Mac shared the moment with the memory of a man who died too young and never got into the Hall of Fame.

As for Sosa, why wouldn't McGwire lift him in a bear hug, shake his hand at first base and laugh at all his jokes in their news conferences? How many of us didn't want to hug Sammy, shake his hand and share his joy? Sosa blew kisses to mom and tapped his heart after homers. Instead of "I am the greatest," he said, "Mac is the man." After his 66th homer, Sosa went home to the Dominican Republic to help hurricane victims.

As Nicklaus walked the back nine on that Sunday at Augusta National, his biggest problem wasn't the golf course but his emotions. That was our problem, too. Amid the ovations in the pines, Nicklaus fought back tears. Except a couple of times when he leaked a little.

On every putt, Nicklaus's caddie whispered, "Keep your head still." The last tap-in was only six inches--for a back-nine 30. "Keep your head still," Jack Nicklaus Jr. said to his father, one last time. "I can handle this one," dad said. Back in the pressroom, many a writer said aloud, "I don't know if I can handle this one."

For come-from-behind shock, for ridiculous joy, for one-day impact and for the universal affection/reverence that America felt toward him, Nicklaus's win seemed more powerful than any event I ever attended. Most of all, however, he had defied age itself, our most implacable enemy. So his win made the whole world feel young. Whatever you thought you'd never do, or never do again, Nicklaus made you reconsider.

If sports were medicine, then Jack's Masters would have been the ultimate tonic. The chase of '98, which consumed headlines for months, was more a summer-long cure for the chronically jaded soul of sport. It wasn't about greed, violence, drugs or strikes. Instead, it celebrated the game's rich past while embracing friendship, sportsmanship and diversity in the present. Mac and Sammy were "I'm okay, you're okay" incarnate. America thought, "That's us at our best."

The illusion of significance is essential to sports. When we're in the park, screaming and rooting, it seems nothing could be more important.

Of course, if tapped on the shoulder, we'd say, "I know, 'It's just a game.' Now, excuse me while I go crazy again." Sometimes, however, sports events actually do have weight. Years from now, we'll know that what Mac and Jack and Sammy did was truly heavy. Because every time we think of them, we'll suddenly feel light.

Thomas Boswell has covered sports for The Washington Post since 1971.

CAPTION: Friendly rivals all the way to their final home run totals.