Acceptance of impermanence as the right of passage to adulthood? My take on Buddha's teaching

My roshi's roshi walked into the parlor where his roshi's (my great-grand roshi if you will) body was laid out. He began to cry inconsolably at the loss of his teacher. All in attendance were dumbfounded. How could a man so deeply awake be so emotional! After all, isn't death just another example of impermanence? Seeing the minds of the other mourners written blatantly in their faces, the man said - "My teacher, who I loved like a father, has died. If I want to cry, I'm going to cry."

Who had the more intimate understanding of impermanence? The man who wept or those who wondered at his weeping?

Your point about becoming an adult is valid. In one sense, Enlightenment is attainment of the Universal Adulthood.

However, accepting impermanence ("and all the **** life throws at us") is not sufficient to get there.

The state of adulthood, unlike that of a child, is characterized by independence -- the strength and wisdom to determine one's life instead of having others (i.e. the adults) determine it for you. Adulthood is a state of self-realization, of being fully and truly oneself.

In Buddhism the obstacles to independence are recognized to be of two kinds: emotional and cognitive. Emotional obstacles are automatic reactions that make us slaves to our emotional neediness, our avoidance of discomfort, and our impulsive irritability and anger. Cognitive obstacles are the ones that make us slaves to our biases, stereotypes, overgeneralizations, jumping to conclusions and other perceptual==>conceptual mistakes.

The complete liberation from both leads to a subjective state that is characterized by a clear understanding of How Things Work, a deep emotional Peace and a sense of Freedom to act according to one's own sound judgement.

It was a dark night, raining lightly, with flashes of lightning. The Buddha said to Ananda: "You can come out with the umbrella over the lamp." Ananda listened, and walked behind the Buddha, with an umbrella over the lamp, [lighting the way for both]. When they reached a place, the Buddha smiled. Ananda said: "The Buddhas don’t smile without a reason. What brings the smile today?" The Buddha said: "That’s right! That’s right! The Buddhas don’t smile without a reason. Now you are following me [while having your own] lamp. I look around, and see everyone doing the same thing." (SA 1150)

...Monks, be your own lamp, be your own refuge, having no other! Let the Dhamma be a lamp and a refuge to you, having no other! (SN 22.43)

The Buddhist path is a gradual training that takes an immature sentient being and sets it on the course of figuring out and getting rid of the emotional and cognitive obstacles to Universal Adulthood, until one attains the state of clarity, peace and freedom.

What do you think? What's the core of Buddha's teachings?

I think the core is the "four noble truths" -- that craving, attachment, and suffering co-arise or are related.

But I don't think there is one core.

Another core is the "Middle Way" -- classically between hedonism and self-mortification; but also e.g. between eternalism and nihilism; or between renunciation and non-self on the one hand, and the brahmaviharas, ethical conduct, and spiritual friends on the other.

Another is the Dhamma being visible, inviting inspection, testable (unlike doctrines of some other religions).

I suspect that anatta is at least as important as impermanence -- and ethics perhaps even more so.

Identifying the mental hindrances or fetters is a core doctrine -- "purify the mind".

Every time we decide to accept impermanence we are Enlightened.

I don't know, maybe it's every time we decide to accept things-as-they-are (which includes "impermanent" -- and that may be one of the harder characteristics to accept, but is not the only characteristic).

“Rāhula, you should truly see any kind of form at all—past, future, or present; internal or external; coarse or fine; inferior or superior; far or near: all form—with right understanding: ‘This is not mine, I am not this, this is not my self.’” --MN62

The Buddha maintained the importance of recognizing impermanence right up into his very last words. It doesn't seem to be enough to formulate your own definition of impermanence, but to see how, in your direct experience, it shows its full authentic nature. The three marks of existence are key: impermanence, suffering and not-self. One should not focus entirely one one domain. Buddha had taught one to see all the three domains concurrently. This is the height of the wisdom he brings out in others from his own wisdom.

Yadanicca sutta

Bahirani sutta