The Sakyamuni’s primary observations
After 7 years of hard slogging through the rotting garbage of archaic religious fiction (mainly the Veda), the Sakyamuni (like any competent scientist) decided to simply observe nature and derive his insights from those observations. His two fundamental insights into the principles of life, obvious now (as then) to anyone person with a brain, were:
“All that is subject to arising is subject to cessation.” To wit, nothing lasts forever.
“A thing arises because of conditions; it ceases when the conditions for its arising cease!” To wit, all things are relative, i.e. without an abiding (i.e. eternal) essence or substance.
In other words, a thing (for instance, a person like you and me) emerges as transient phenomenon from transient and ever changing causes (or conditions). In short, a thing happens as the effect of transient conditions, like a cloud or a wave. Whether or not the conditional effect was supported by an abiding self or core (Pali: atta) he chose not to elaborate.
Distress (Pal: dukkha), he claimed, arose because we cling to that which is impermanent and conditional and therefore which we can’t own. In other words, distress is the response to loss, or to put it more succinctly, the inability to achieve an unconditioned, unchanging and permanent state. That is nonsense.
The solution to ending dukkha initially proposed by the Buddha, i.e. for use by monks but not householders, was the practice of the 4 Jhanas.
And that, initially at least, was that. All further Buddhist philosophy developed from the two initial insights and his dodgy conclusion about the origin of distress.
Note: Both insights are unrelated to morality, i.e. to good or bad works.
This scenario was initially taught to likeminded monks/beggars (Pali: bikkhus) who had dropped out from the everyday world.
The initial solution to overcoming distress was the practice of the 4 Jhanas, and which are essentially distress free coma (i.e. benign sleep) states. A coma state happens if and when full concentration (or mindfulness) is brought to bear upon a single focus to the exclusion of all others. During perfect concentration the brain processes only one data bit and which appears permanent and unchanging. During the practice of the Jhanas the effects of arising and ceasing and of conditionality are suspended and distress cannot happen.
When the Shakyamuni tried to spread his original and very abstract dharma to the general population he quickly realised it wouldn’t work. So he dumbed down his original proposal by offering more obvious and therefore popular causes of distress, such as desire and the facts of personal decay and more popular means for their avoidance.
That desire fulfilled and the achievement of personal growth produce positive stress (Pali: sukka = pleasure or happiness) he chose to understate.