There are times in life where it is important to be selfish. We all have limits that once passed force us to break down ourselves. Just because others want us to occasionally push past those limits, doesn’t mean we should actually do it.
Know your boundaries and set limits appropriate for you. Be selfish about it. Only you know how you can best function. If those limits aren’t acceptable to someone else, that’s their problem. That’s where the selfishness becomes important.