The First Noble Truth with its three aspects is:

1. There is suffering, dukkha.
2. Dukkha should be understood.
3. Dukkha has been [therefore 'can be'] understood.

What is the Noble Truth of Suffering?
(a) Birth is suffering, (b) ageing is suffering, and (c) death is suffering.
(d) Dissociation from the loved is suffering; (e) not to get what one wants is suffering:

(a) to (e) are the five categories of suffering affected [caused] by clinging [or attachment to views].

This Noble Truth must be penetrated by fully understanding suffering.
This Noble Truth has been [can be] penetrated by fully understanding suffering:
Such was the vision, insight, wisdom, knowing, and light that arose in me about things not heard before. (Samyutta Nikaya LVI, 11)

This is a very skilful teaching because it is expressed in a simple formula which is easy to remember, and it applies to everything that you can possibly experience or do or think concerning the past, the present or the future.

The Pali word, dukkha, means 'incapable of satisfying' or 'not able to beat or withstand anything'; always changing, incapable of truly fulfilling us or making us happy.
The sensual world is like that. Contrary to our impulse instinct or first assumptions it would, in fact, be terrible if we did find satisfaction in the sensory world - because then we wouldn't search beyond it; we'd just be bound to it.
However, as we awaken to this dukkha, we begin to find the way out and are no longer constantly trapped in sensory consciousness.