One of the core ethical questions is “Why should I or why should we be good?” And what does “good” even mean?
The question of why I or we should be good calls forth two different meanings of “good”:  goodness as an individual and goodness as a kind of social wellbeing. There is an underlying assumption that being good means “good” for someone or something and thereby a reference to human actions is presupposed. Before answering this question, the conditions of moral responsibility for each and everyone must be established first: I am morally responsible for my behaviour if I choose my behaviour freely (not acting under duress) and if I act knowingly (with respect to the difference between right and wrong). While the question of “we” alludes to society at large, the question of why “I” should be good puts the moral responsibility where it belongs in the first place: on me and my innate faculty of judgement1.

Thus, why should I be good? When trying to answer such a fundamental question, one must look at the conditio humana. “I” am an inescapable part of myself (personally) and a part of a larger group or a member of society (impersonally). Hence, I have to live with myself and with others albeit a temporary escape from the latter is possible at times. But what I can never escape from is the „inner judge” who plays the role of an „impartial spectator” as Adam Smith pointed out in his Theory of Moral Sentiments2. In his line of thinking, man may evade the public mirror of society by avoiding social contact but he cannot escape his own inner mirror by which he examines the propriety of his own conduct. If this ability of introspection is an intricate part of human nature, my self-perception is an integral part of my self-esteem.
For me, being good means being confident with myself and being mentally strong. Feeling good with myself. According to Plato, “good” denotes the mental order of the individual (Plato’s Cave Allegory in the Politeia 518d). Thus, in a way “being good” depends on my inner being which acts out for others to feel and see. If I am confident and mentally strong, then I am able to take a back seat when necessary, to solely focus on the matter at hand and to protect myself from within by building resilience. To put this argument in a formal fashion:

P1: My thinking and behaviour reflects on my own wellbeing.
P2: If I’m confident and mentally strong, I’ll be more capable going through life and tackling everything life may throw at me.
C:   My wellbeing ensues from my being good.

Even without any moral obligation, being good in that way pays off in every respect. However, this core ethical question of why I should be good yields an implication of the moral responsibility of moral agents. As sentient and rational beings, humans have an interest in their own wellbeing be it due to moral, religious or political reasons. In Plato’s line of thinking, man lives happily when he leads a good life (ευ ζῶν) (353ef./580c), when his constitution is in order (Philebos 11d).
In order to lead a good life with myself I have the obligation to work on myself as a person and thereby finding my true self.3 This is by no means an easy feat but an important part of our humanitas in Ciceronian sense (παιδεία as mental culture and φιλανθρωπία as humanity/humane feeling).
“Being good” means starting with myself to make a difference in the world, i.e. to stop spreading evil by letting insecurities fester within which then may turn some people into spiteful human beings towards others. We as moral agents should take that challenge upon us even though it is no easy walk for sure – for the sake of others and for ourselves.

1 See Kant: Critique of Judgement.

2 Adam Smith: Theory of Moral Sentiments. P. 135.

3 See Nietzsche’s self-education in Schopenhauer as educator and Thus spoke Zarathustra.