It's clear you shouldn't overspend when you have no security of the future salary cap variations. As the world/a country's economy can enter a difficult period abruptly, the same can happen in every financial situation in sports where changes can arise.
That's why we must value what we have in our front office and sometimes people bashing Ainge (for example, for not trading for Ibaka or PJ Tucker last deadline) should realize. We are in very good hands, the pros clearly overcome the cons.