An integral looks at accumulation across a span. A single point can be dramatic and still tell you very little about the whole curve. The same is true of a life. Identity is built through thousands of small pieces: what you repeatedly notice, avoid, practise, tolerate, say, withhold, and return to.
The concept also refuses to count every hour as equal. Some periods of life are fully inhabited. Others pass with very little of you actually present inside them. A week can be busy and leave almost no trace. One quiet afternoon can alter the next ten years because something finally enters deeply enough to change the person who continues.
Then there are singularities: grief, betrayal, illness, love, rupture, revelation. A huge spike can bend the curve without becoming the whole curve. Integration means the event remains real while gradually losing the power to define every point that comes after it.
If the last month were an area under a curve, which ordinary hours built most of it?