When paint peels down to bare wood, the cause is usually moisture getting behind it. That moisture can come from outside, through failed caulk, open joints, or soft trim, or from inside the house, especially near bathrooms and kitchens without good ventilation. Painting over it without fixing the source just restarts the clock.
Peeling between layers is a different problem. On older homes with many coats, a new layer can lose its grip on a chalky or glossy old finish that was never cleaned or scuffed. This is why washing and sanding matter even when the old paint looks sound.
A lasting repaint follows a simple order: wash the surface, scrape and sand everything that's loose, repair or replace rotted wood, re-caulk open joints, spot-prime bare wood, and only then apply finish coats. Skipping any of those steps saves a day now and costs a repaint later.
If your house has paint that keeps failing in the same spots, look at those areas first. A worn sill, a missing piece of flashing, or a gutter that overflows onto the trim is often the real reason, and it's usually a small carpentry fix.