Shyness is Coward; prompted.

Shyness is Coward; prompted.
In abhidhamma, minds and mental factor of sasaṅkhārika (prompted) mind is coward.

What is sasaṅkhārika (prompted)? (src)

12. Sankhārika-
    This is purely a technical term used in a specific sense in the Abhidhamma. It is formed of 'sam', well and Ö 'kar', to do, to prepare, to accomplish. Literally, it means accomplishing, preparing, arranging.
    Like dhamma, sankhāra also is a multi-significant term. Its precise meaning is to be understood according to the context.
    When used as one of the five 'aggregates' (pañcakkhandha), it refers to all the mental states, except vedanā and saññā. In the paticca-samuppāda it is applied to all moral and immoral activities, good and bad thoughts. When sankhāra is used to signify that which is subject to change, sorrow, etc., it is invariably applied to all conditioned things.
    In this particular instance the term is used with 'sa' = co-; and a = un, Sa-sankhārika (lit., with effort) is that which is prompted, instigated, or induced by oneself or by another. 'Asankhārika' (lit., without effort) is that which is thus unaffected, but done spontaneously.
    If, for instance, one does an act, induced by another, or after much deliberation or premeditation on one's part, then it is sa-sankhārika. If, on the contrary, one does it instantly without any external or internal inducement, or any premeditation, then it is asankhārika.

How can the practitioner comprehends shyness?

the practitioner must comprehends below mind, it's mental factors, and the matters born of those mind&mental factors to comprehend shyness:

4 prompted attaching mind (src)

Attaching consciousness, prompted, accompanied by pleasure, connected with wrong view,
Attaching consciousness, prompted, accompanied by pleasure, disconnected with wrong view
Attaching consciousness, prompted, accompanied by indifference, connected with wrong view
Attaching consciousness, prompted, accompanied by indifference, disconnected with wrong view

Mental factors: Twenty-two factors enter into combination - namely, thirteen aññasamānas, and 3 greed mental factors, 2 boring mental factors, and 4 ignorant mental factors (13 + 3 + 2 + 4 = 22)

1 prompted rudeness mind (src)

Rudeness consciousness, prompted, accompanied by displeasure, connected with ill-will

Mental factors: Twenty-two factors enter into combination - namely, twelve aññasamānas, and 4 angry mental factors, 2 boring mental factors, and 4 ignorant mental factors (12 + 4 + 2 + 4 = 22)

12 prompted wholesome mind (src)

Beautiful consciousness, prompted, accompanied by pleasure, associated with knowledge. x3 (wholesome, resultant, kiriyā)
Beautiful consciousness, prompted, accompanied by pleasure, dissociated with knowledge, x3
Beautiful consciousness, prompted, accompanied by indifference, associated with knowledge,x3
Beautiful consciousness, prompted, accompanied by indifference, dissociated with knowledge.x3

Mental factors: thirty-six factors enter into combination - namely, thirteen aññasamānas, and twenty-five beautiful mental factors (13 + 25 = 38)