It wasn't an arbitrary upswing. Hellenistic period lasted a good 300 years, and there was a decent prelude to it. Note the civilizations that came after it, although great in their own right. Including the Roman civilization had its own goals(Territorial expansion, cities, entertainment, Urban living etc etc).
Now to give you another example as to how things could reverse and take forever to recover. Take a look at USSR and its space program. They were once in race to putting man on the moon and sending probes to Venus. Today? Not really that ahead of the pack.
NASA on the other hand, has had relatively a lot more success. But a lot could change if there is some unanticipated political or economic crisis that could set back US as a country. Of course a new country will likely replace it, but the end and start points won't be exactly the same.
The point being you need continuity and need to keep the inertia going to achieve stellar growth.
Now to give you another example as to how things could reverse and take forever to recover. Take a look at USSR and its space program. They were once in race to putting man on the moon and sending probes to Venus. Today? Not really that ahead of the pack.
NASA on the other hand, has had relatively a lot more success. But a lot could change if there is some unanticipated political or economic crisis that could set back US as a country. Of course a new country will likely replace it, but the end and start points won't be exactly the same.
The point being you need continuity and need to keep the inertia going to achieve stellar growth.