I can think of no better illustration of what selfishness is than "refusing to inconvenience oneself to help the less fortunate or more vulnerable."
The rich refusing to give a meagre portion of their wealth to help the poor. They justify it by saying "The poor will be happier if they rely on themselves instead of asking for handouts" - but the selfish can always justify their selfishness.
Racial majorities refusing to question or challenge the systems that help them but hurt minorities. They justify it by saying "Minorities are already equal, they just have to take responsibility for their own situations" - but the selfish can always justify their selfishness.
Healthy people will refuse the minor inconvenience of a vaccine or a mask in order to protect the most vulnerable in the population. They justify it saying "Immune compromised people and their loved ones should protect themselves with better protective equipment and isolation, instead of depending on the rest of society to keep them safe" - but the selfish can always justify their selfishness.
I think that's the true cowardice inherent in selfishness - it never admits its own character. The selfish almost always couch what they do in justifications and rationalisations because looking at oneself and admitting one's own selfishness is intensely uncomfortable.
And the selfish have no tolerance for discomfort.