Selfishness

Life is a funny thing. Selfishness comes easily; maybe even naturally, and probably has been necessary for survival for life in general forever.
Where do we draw the line between what is acceptable selfishness and what  is excessive?
It seems obvious that opinions will vary on this just like any other subject.
The different aspects of selfishness are interesting to me and I am wanting to explore them by writing some of them down.
It has occurred to me at work that I would rather be home or somewhere else doing what I want. I often think of retirement, though it is (hopefully) eight years away.
It might be selfish of me when I think these thoughts. I can help other people at my job and the effects of my job may be far-reaching.
Any job might have far-reaching effects on others. Simply the way we interact with people may profoundly affect them.
I am sure that many people are taught “look out for number one no matter what”, and it could be taken as anything from eating right and exercising to pushing people out of the way for no reason whatsoever.
So is a clear definition of what is selfish and what is not, too complicated to write about in a few sentences?
Probably.