I'd even argue that it's natural - when you break down the word, what you're prioritising here is yourself. While maybe not consciously, you will be doing most things with yourself as a priority first, for your present and future maintenance, and ultimately your own wellbeing. And this isn't evil or wrong, it's just human nature. We're all selfish in this way, so we shouldn't be scared of the label or understand selfishness to be an inherently bad thing.
While maybe not consciously, you will be doing most things with yourself as a priority first
If you're completely ignorant of the negative impact of your actions on the people around you, then this is obviously a different story. But we all have needs that we can acknowledge, and there are so many ways we can and do fulfil these on a regular basis, without inflicting harm on to others. Our actions can be centred around ourselves ('selfish') in a gentle and thoughtful way.
needs that we can... fulfil... without inflicting harm on to others
Say you've cancelled plans to sit at home and do your uni work. Realistically, nobody's going to call you selfish for this, it'd be ridiculous to categorise you as a bad person for prioritising something as important as your future. But technically, it fits the definition, if you're putting your needs before your friends. In practice, your friends may be temporarily disappointed, but there's quite obviously something more important at play and they'd more than likely empathise with you here. This is why the concept of selfishness needs to be re-evaluated and not be confined to having exclusively negative implications.