Selfish. Wouldn't you agree that there's a limit to how much space the world and its inhabitants are willing to give up to accommodate you? Especially if the space is considered their "personal space?" Aren't we being stripped of the luxuries that used to come with being a member of a community? The luxuries of being able to freely walk and occupy some geography for a given period of time?

Wouldn't you also agree that human families, over the ages, have grown smaller? Especially in the West and the Westernised. Over time, folks have given birth to fewer children for whatever reason.

Here's my proposal: these two observations are inherently connected. The fewer people a human has to deal with whilst growing up, the more interested such a human is in "personal space." Say the number of people dealt with growing up is Np and the fellow's interest in personal space is Pi then, the relationship is given by:
 Np ➰ 1/Pi
Therefore Np = k/Pi

Where k is a geographical constant which is defined as the total surface area of the earth.

PS: Of course this is an untested hypothesis. But a hypothesis nonetheless.

Ẹnìkan kìí jẹ́ àwádẹ́, àjèjì ọwọ́ kan kò gbẹ́rù dé orí, àgbájọ ọwọ́ la fí sọ̀yà.