This has been one of Shaquille O’Neal’s eternal vanities. One of several, but perhaps the most germane to his team winning or losing.

His insistence, throughout his career, that everyone stop talking about his inability to make free throws because he “will make them when they matter.” At some future point in time.

Well, making them could hardly matter more than the past week-plus, when the Phoenix Suns’ future hinged on the Big Cactus being at least remotely acceptable from the line.

And, of course, Shaq was as awful as usual. Arguably, the difference in the series all by his awkward self, chucking free throws in the general vicinity of the backboard.

Shaq made 32-of-64 free throws, or 50 percent. That actually is below his regular-season average of .513 or his career average of 52.4.

San Antonio invited Shaq to beat it at the line, and he couldn’t. The Spurs fouled O’Neal repeatedly, employing the hack-a-Shaq strategy in several games, with good results.

As we have noted, he missed 11-of-20 in Game 5, a game the Suns lost by five points.

He missed 7-of-13 in Game 2, which the Suns lost by six points.

And he missed 2-of-3 in Game 1, the double-overtime game the Suns lost by two. (Before Spurs coach Gregg Popovich came to the conclusion that fouling Shaq was a huge advantage for his team.)

Making them when they matter? Could it matter more than in this series, which probably will be the turning point in Suns franchise history? When their window of opportunity for winning their first NBA title probably just slammed shut?

Shaq will be 37 next season. Grant Hill will be 36. Steve Nash will be 35, which is like 45, in point guard years. (Nash was destroyed by Tony Parker in this series, by the way.) The likelihood of the Suns winning 50 games again next season and posing a real threat in the playoffs … probably is over.

Plus, consider that they owe Shaq $20 million each of the next two seasons. That huge bill will hamstring the Suns, perhaps cripple them for two years — until they can get him off their payroll. His expiring contract might actually make him attractive, in 2009-10 … but for now? The rest of the league is going to say “no, thanks.”

Don’t get me wrong. I don’t dislike Shaquille O’Neal. I always preferred Kobe Bryant in the Shaq-Kobe Lakers feud because Kobe clearly had more upside for far longer than did Shaq. But that didn’t mean Shaq was a guy it was easy to dislike. He wasn’t. He isn’t. He can be childish and petulant, but on the whole he is accommodating, mentally acute and highly amusing. He is a friendly guy who means well.

In his prime, he was a force of nature. A giant of a man who scared that bejeezus out of the rest of the league for more than a decade. To rile him was like tugging on Superman’s cape.

He is one of the great players in NBA history. But he is not one of the truly elite and never will be because he had this Achilles heel … or more like an Achilles leg — his inability to make free throws, which led to his teams’ being hamstrung in crucial situations … which led him to be benched in crunch time simply because his teams didn’t want him at the line.

None of us does everything well, even within our chosen professions. Shaquille O’Neal, so good in so many aspects of basketball … had one enormous, glaring, never-to-be-forgotten (or minimized) flaw that will follow him into history.

It wasn’t the Suns who saw their “championship window” shut last night. It was Shaq, too. It’s hard to imagine him winning that fifth ring — unless he’s willing to be a backup, a role player for some other team, at a severely reduced salary, and his pride almost certainly will not allow that.