i'll write this topic top off my head , so, excuse me for any mistake or insufficiency of the topic

EXTERNALITY

in a simple meaning.. it is an effect which occurs to third party from an act or omission from two parties

nothing's left to say .. but if you look at it deeply and think about it
it has a great effect on the society

the most simple and "childish" example for externality is when you have a fight with someone else
that someone else's friends.. in consequence become your enemies

although you haven't harm them.. but it is the externality's effect

now , let's get serious and try to understand

In Japan , when they had earthquake
unlike us ,they went to markets and bought water and food what's enough for one day
ONE DAY ONLY

why ? because they do understand the prices will go up if they all went and bought what they could
to save theirselves from hunger and thirst

how come this is relevant to externality
?

simply, most of them are capable of purchasing necessary food and water .. but others will suffer from two things
lack of such food and the high prices of the such food

the externality , i purchased food at crisis
it is a deal between me and the seller

but others people who are subsequent to my purchase gor affect
if i was selfish and didn't think of them..they will suffer

that's what happened in Japan.. everyone was concerned about the others not themselves
and that's by Self-Regulation not governmental one

what happened here in Juno and Phet
everyone sought for themselves only.. everyone bought a lot of food and water

and that . cause real problems to another

why ? becuase the lack of understanding the concept EXTERNALITY

that's at national level

how about individual level

have you ever thought your deed will affect other people
?

indirectly or directly, everyone in your society will get affected by your deed
by your action.. your omission of doing something you should have done

isn't that a good reason for us to think before act
??

only smart and wise people who put externality in thier considerations
they realize their actions will affect other in one way or another
and they are very careful to act , their action could lead others to do the same or the contrary

in sense, if i helped someone in anyway, the externality of that someone else will help others
it is not condition but it is usually the case
it is encouraging others to act as the way you do
or the contrary as i mentioned above

look at it as a domino
your action will push the first piece.. and you could imagine the externality of your act now
all other pieces will be affected

more lovely image , if you are a diamond and the good externality you create the clearer you are
when lights go through you , lights as deeds done by you
it will spread it to others in nice way , colorful lights for all people around you

but if you were source of bad externality
others , won't get benefit, but they will be annoyed by the lights you mirrored to them


it is a huge concept cannot be explained or described in one thread


the bottom line is

think of your actions and think of the externality of your actions

believe it or not
one action could change the world..

and all that just because of externality