People who dismiss ASEAN as an ineffectual "talking shop" make a big mistake.
But so do those who assume ASEAN will forever provide the answer to every strategic or diplomatic question in South-east Asia.
Like any institution, ASEAN's success has been a product of its circumstances and, as circumstances change, its future is not assured.
ASEAN's most important achievement can be easy to overlook because it has been so successful.
It has created and upheld the principle that its members do not use or threaten force against one another.
We have to remember how far this was from being true in the 1960s - and how far it is from being true in so many other parts of the world today - to see how remarkable that achievement really is.
The few occasions on which this principle has been violated only help to show how widely it has been respected.
Of course, ASEAN has done much more than that, particularly in promoting economic, social and political engagement among its members. But all of these achievements depend on ASEAN's primary legacy - peaceful interrelationships.
Keys to ASEAN's success
How did this happen? One reason of course is the statesmanship of a remarkable group of leaders among ASEAN's original members.
Typified by men like former Singapore prime minister Lee Kuan Yew and former Indonesian president Suharto, they had the vision to see how much their countries stood to gain by cooperation, and how much they had to lose from rivalry.
But that was not enough by itself. ASEAN's success also depended on a very favourable strategic environment in the wider Asia-Pacific region.
It is no coincidence that ASEAN was founded just as developments on the battlefield were about to weaken American public support for continued military action in Vietnam.
As Mr Lee has said, the United States' stand against communism in Vietnam gave ASEAN's first members the chance to consolidate their post-colonial political and economic systems, without which ASEAN could not have worked.
But more than that, the end of the Vietnam War also marked the end of the strategic rivalry between the US and China, which had fomented conflict in South-east Asia for two decades.
When then US President Richard Nixon met Chinese leader Mao Zedong in 1972, they ushered in a new regional, strategic and political order in which, for the first time, US primacy was uncontested by any major Asian power.
This provided the foundation for a remarkable era of peace and stability throughout East Asia because it banished the great power rivalries which had been the engine of so much regional conflict for centuries.
This has been vital to ASEAN's success because it has removed a potent source of discord between its members.
Strategic rivalry between great powers invariably leads them to compete for influence over smaller countries, as China and the US did in Southeast Asia during the Cold War.
ASEAN would not have flourished if China and the US had remained strategic rivals because they would have continued to try to divide ASEAN members against one another by drawing them into their competing spheres of influence.