There are two aspects to the First Noble Truth.
1. There is hidden suffering in attaching to worldly things. An average human thinks highly of kama assada or sensory pleasures. But because of their tendency to do “whatever it takes” to fulfill sensory desires, average humans are tempted to do immoral things.
– Some people think they will not do immoral things. But that is only because they have not been subjected to high-enough temptation.
2. Because of the above, average humans inevitably are reborn in the four realms at some point in the future. Suffering in those realms is worse than the suffering endured by ANY human.
That is one version of the “previously unheard Dhamma” of the Buddha.
– Even though they may get a temporary sensory satisfaction by “somehow fulfilling those desires” they pay for that when they are reborn in the apayas.
A good analogy is a fish biting a tasty bait. There is a momentary pleasure (when seeing the tasty bait), followed by unbearable suffering.
– But unlike in that case, suffering in the rebirth process is not immediate.