Of all the mysteries that professional golfers try to fathom, none is more constant, or more nettlesome, than trying to decide why, among players of apparently similar ability, some win and some don't.

On tour, the difference between one man and another is almost infinitesimal. At every level of the sport, from top stars to middling veterans to rabbits, there are countless inexplicable cases of men taking demonstrably similar games and getting almost completely different results in both fame and fortune.

In 1981, for instance, Bill Rogers was player of the year, yet his scoring average was just one-tenth of a stroke per round better than anonymous Bob Murphy, who won nothing and was 49th on the money list. Murphy even played in more tournaments.

Tom Watson's stroke average was just .03 better than Bobby Clampett's, yet Watson won twice as much money. Ben Crenshaw, who has never won a major tournament, actually had a slightly better Vardon rating than Rogers, yet won no tournaments to Rogers' four and finished 15 spots behind Rogers on the money list.

In golf, the differences are tormentingly tiny; over a full season like '81, the gap between being Jack Nicklaus and being Brad Bryant (80th in money) is exactly one stroke a round.

As a result, one question underlies all others on Tour: how do you translate shot-making talent into victory, whether you measure winning in terms of U.S. Open titles or merely in making cuts and earning a living?

"I'm always asked, 'Who'll be the next great young players,' " says Jack Nicklaus, golf's foremost authority on what it takes to win. "Gee, I run into a new one every week who's better than the last one--John Cook, Bobby Clampett, Fred Couples, Mark O'Meara. One may have the best-looking swing, yet this other one over here is winning more.

"It's hard to tell which ones will have the really substantial careers," said Nicklaus. "I was fortunate. When I came on Tour (in '62), I was lucky enough to win (the U.S. Open) right away. First, you have to learn how to win. Then, that breeds more winning and it gets a lot easier.

"But, before you learn to win, you have to learn to lose. Look at Tom Watson. He had to lose big tournaments and, then, learn how not to make those same mistakes again. When that happens to a guy, like Tom, he becomes one of the dominant forces."

Even now, Nicklaus worries about what it takes to win. "Being asked, 'Can you still win?' is a constant irritation factor. It's been there for me since I turned 30 and had my first (two-year) slump. You have to constantly stand up for yourself. And answer to yourself. Even this spring, when I was got close several times, I couldn't finish the tournament.

"In the long run, the aggravation is probably good for you. It makes you go to work, rework what you have . . . If you don't change your game, then your career doesn't last too long," says Nicklaus, who, at 40, built both a new full swing and a new short game. In the last few months, at age 42, he also has completely taken apart and reassembled his once unparalleled putting stroke.

Pros constantly study each other, looking for clues. Take Mark McCumber, who has won one Tour title, but must struggle annually to stay in the top 100.

"They say you have to 'enjoy your work,' " he says, "but it's hard to find just the right balance between the enjoying and the working. If you don't feel the game as a pleasure, you can't play well, but if you don't work very hard, you don't improve.

"This year at Bay Hill, I shot 69-72 to make the cut," says McCumber. "As I was leaving the course, feeling happy, I saw Tom Kite (who'd shot 69-70) still out on the range at dark. He wasn't satisfied. Kite went on to (shoot 70-69 and) win the tournament." McCumber doesn't mention that he finished 72-76 and finished 37th.

That balance between labor and love is a constant torment. "Just last month, I asked myself, 'How much fun are you really having?' " says the promising Cook, 24. "I was hitting too many balls, listening to too many other players' problems, spending too many hours at the course. I decided just to enjoy myself."

Then, in the next breath, Cook says, "It takes several years to gather momentum, keep improving. Look at Watson's constant trial and error, all the hours he puts in practicing."

Even Nicklaus admits he burned himself out this spring with too much tinkering and too many tournaments. "After the Masters, I told (his wife) Barbara, 'I'm going to enjoy the next couple of months, just relax.' I was pressing so hard that I never had less than 34 putts," said Nicklaus who, on Friday, had 28 putts. "You say, 'I'll just nail it at everything and see what happens.' Give it a little of the 'I don't give a darn.'

"That (relaxed) attitude is probably why I've shot so many good final rounds over the years when I started the day a few shots behind with nothing to lose . . . (pause) . . . and maybe that's why I've shot so many bad last rounds when I was ahead and knew I couldn't afford a mistake."

The pressure of actually winning a tournament is so great that some young players almost pretend they're not in contention when they actually are.

"The first tournament I ever won, I shouldn't have," says George Burns of his one Tour win in the '80 Crosby. "It helps to be around the lead a few times, then stumble upon it, like I did."

"Look at Jerry Pate at the '76 Open. He deserved to win the week before at Philadelphia, but he didn't. Then, at the Open, (John) Mahaffey had the pressure on him all week for 70 holes (as the leader), then Pate popped up in the last couple of holes and won. If you hang around the lead often enough, you'll get the break you deserve.

"Right now, there are only a few players who, on the last few holes can just take charge and win--Nicklaus, Watson, Pate and maybe Craig (Stadler) now that he's won the Masters," continued Burns. "Ray Floyd can also sniff the lead and grab a tournament. Tom Kite's consistent but maybe not quite in that category yet."

In other words, many pros, at least in part, need to have victory fall into their laps. The few don't have that need, but they matured by a hard process. Stadler, for one, has gradually gained control of his temper. He also has learned a couple of optional swing patterns, like the draw he's using this week. He turns to that swing when his usual game temporarily deserts him.

"It takes years to get experience," says Lon Hinkle. "In fact, I think the more success you had before you turn pro, the harder it is after. Some guys can't take being 'just another player.'

"To actually win a tournament, that takes all the tangibles you can put your finger on, plus. Plus what? I'm not exactly sure what it is. I only have three (Tour) wins. But it's something in your head that filters down into your game."

Those thousand and one head games are the pros' fascination, and their bane.

"We're creatures of habit," says Gibby Gilbert, 41. "When I find a place I play well, I just keep going back every year, whether I know the reason why or not. Dale Douglass and I are the only two people who have played in all 15 Kemper Opens. I even play well in the Kemper when they change the site.

"As you get older, it gets harder to win than just to contend because it seems you can't shoot those real low scores anymore. I used to have a 62 or 63 some place every year. I couldn't shoot a 62 now if they let me play in a onesome with three pencils," continued Gilbert.

Life on Tour is a constant struggle for a winning edge, either in technique, equipment, or, especially, state of mind. Sometimes, that margin--whether it's the one stroke difference that makes the cut or the shot that wins the whole tournament--can seem so thin that the tormented men of golf actually begin to doubt its existence.

"What does it take to win out here?" said soaking wet Mike Nicolette yesterday as he tried to dry off during a rain delay at the Kemper. "How would I know? So far, I can't even earn a living."