Why does blood pressure need treating if you feel completely fine?

Because it causes damage silently for years before producing symptoms — the reason it is called a silent condition is that the first symptom is often the stroke or heart attack itself. Sustained high pressure damages arteries, the heart, kidneys, eyes and brain gradually. Feeling fine is expected rather than reassuring. This is also why adherence to treatment is poor: there is no immediate feedback for taking the tablet, and no immediate consequence for skipping it. Practical fixes include once-daily combination tablets, linking the dose to an existing routine, and home monitoring, which makes the invisible visible.