First aid is the bridge between an emergency and professional medical care — the interventions that can preserve life, prevent harm from worsening, or reduce permanent damage in the minutes before help arrives. Knowing how to recognize a medical emergency (cardiac arrest, stroke, severe allergic reaction, choking), what to do and what not to do, and how to summon appropriate help is a form of bodily knowledge that should be as universal as literacy. Every person capable of learning basic first aid should — the life it saves is as likely to be someone you love as a stranger.
Each step builds on the last.