If you’re characters aren’t authentic, your story will be flat. The best way to write authentic characters? When presented with a difficult situation in real life, almost everyone will instinctively behave in a selfish way.
When they don’t, it makes readers call bulls**t. Several legendary stories have really bad cases of characters behaving selflessly to the point of ridiculousness. Robinson Crusoe and 20,000 Leagues under the Sea are the first to come to mind. Back in the day, writers loved to portray the idea of the National Myth. That means writers used to have characters from other countries selflessly devote themselves to the character of their nationality. These books are still fun to read, but it shows a certain old-timeyness that doesn’t relate to modern readers.
Make your characters selfish. At least a little bit. It’s OK. To some degree, it’s how we all operate, right? Money’s tight, you don’t give it out to other people. Food is scarce, you gotta make sure you don’t starve. Danger presents itself, you ask, is this worth it, or should I bail?
You can make some characters more or less selfish than others, but someone who walks around with no concern for themselves, well, that’s a fictional person. And probably not the kind you want kickin around in your story.
Thanks for reading!