I'm building a small chat. Now I see but in other chats (whatsapp, facebook mobile chat, sms ...) that the arrangement is always the same:
Left: the chat partner. right: myself
Why is that?
If you look at most languages they are from left to right and the basic concept of a chat is about mutual interaction based upon the person's previous response. Hence, your responses will be driven by the response of your chat partner and hence his response is placed on the left and your response on the right since your response is driven by what he has said.
I would also recommend reading upon F shape patterns in reading since what you see here is a classic example of users utilzing the F shaped pattern to go through information i.e.
Also another question might be asked as to why the user responses are not on the same line.While the reason would be mainly due to the limited real estate spaced offered by mobiles, I also believe the fact the top left and bottom right are the primary areas of focus as the user scans across content. This is best illustrated by the Gutenberg principle of terminal areas which has this to say :
Ok, why is your chat is always right, and the partner is left, In English you read form left to right, therefore, your focus on reading will be in your partner parts, not yours because you already know what you wrote. hence, your eyes keep looking in the left to read in comfortable way, and the other reason is to divide your msgs and partner msgs.