Perhaps you’ve forgotten. It is one of the best excuses ever! “I forgot.” Let’s examine this idea. Remembering may be helpful.

Remember implies that a thing exists in the memory, not that it is actually present in the thoughts at the moment, but that it recurs without effort. Recollect means that a fact, forgotten or partially lost to memory, is after some effort recalled and present to the mind. Remembrance is the store-house, recollection the act of culling out this article and that from the repository. He remembers everything he hears, and can recollect any statement when called on. The words, however, are often confounded, and we say we cannot remember a thing when we mean we cannot recollect it. [Century Dictionary, 1895]
Source: Online Etymology Dictionary

Take a step back. See if you can remember how you were somehow separated from your original tribe. There you were, alone in a hostile environment, somehow managing to dodge every peril while seeking food and shelter. How you thanked the great spirits for sunset and rain, the relief from the heat of the day, and the promise of fresh water often enough to keep you alive. Then you found it, the opening to a cave. Fearful of the unknown, you stood outside and called into the cave, listening intently for any sign of life, anything more than an echo. Your sole possession, that animal skin offering so little comfort against the elements was no fashion statement, simply one of the few necessities of life. Having seen yourself only in pools of water, you harbored no concerns about being judged on appearance. Your hope was to find more like you and what was that? Voices, yes! Human voices responding to your call. Hallelujah! Redemption was nigh.

Women emerged from the depths of that cavernous dwelling. One of them took you by the hand as another slipped her arm around your waist, the others cautiously, thoroughly, surrounding and inspecting you. They sounded their concern and approval of your appearance and your arrival. You were taken in and immediately offered water, as they considered your countenance and your plight.

Perhaps you have forgotten the initial communication around you, about you, the fuss over you. And they allowed you to sit, though there was so much to do. Straws were drawn to find which of the women would continue to tend to your needs as the others returned to their chores. Making the most of their domicile was rewarding work, compared to the tedium of waiting for the men to return with their quarry. 

Why was there no decision to be made about your inductance? Because you are one of us. That is enough reason for people like us to care for one another. It is normal. Your membership simply makes sense. (Re-membership?)

The men return with their kill, having managed to bring home food, successfully avoiding the prospect of being food for the very animals they hunt daily. They are happy to see there is a new member of their tribe. Again you will be considered, not judged on your looks or by your popularity, celebrity, or personality, but simply by the implicit value of “one more” in the mundane world of daily survival. We are made stronger, and better now by your presence. This is obvious and requires no pronouncement. The tribe expresses contentment, there’s a scant need for joy or celebration. And you know your value, your contribution is assumed and you are happy to oblige. 

Has evolution washed away these memories? Let’s see. How do you survive today? When were you last alone and searching for food, shelter, and the comfort of your tribe? Moreover, how did you behave and what were your contributions when you encountered another member? Given the choice of cooperation or competition, how did you plan for that event? These and other considerations are the beginning of this long story. Being nice is normal. Rewards for the simplest kindness are immediate and always available to those who possess even a modicum of awareness. If you ever feel like or think that you don’t know what to do, just remember the day you arrived at that cave and the relief and elation of being taken in by people like you.

People like you.