I'm mulling this over, and I suppose I think the question is, 'if resilience is the most inportant quality to have, what is it important for?'. In other words, what kind of idea about human flourishing is underpinning the notion that resilience is the most imoortant quality?
One thing we might say is that this is a utilitarian view of human flourishing. Rather than asking 'what is the best quality we might possess', or 'what is the most noble quality we might possess' or 'what is the most virtuous quality we might possess', the idea of an important quality suggests that it is important for some purpose: succeeding in life, maybe; being happy; achieving your goals. For all these, I think we could agree that resilience probably is very important.
But what about if your idea of human flourishing is different: if it is to live a good life, or to live a virtuous life, or an honourable life, or a devout life? Then you will ask different questions: how can I be good? What is necessary to be virtuous? How can I behave honourably? How can I make God's will my own? And if those are your questions then you will end up with very different qualities that seem desirable.
What I am saying, I suppose, is that resilience is the the 'best' quality for a self-defined, materialistic, happiness-obsessed age. Each age finds its own ideals, and perhaps resilience is ours. But, speaking for myself, I find it a shallow and limited one.