Peeling is for bananas, but not for paint. Peeling exterior paint is all too common a find during home inspections here in Connecticut. Take for example this dormer, one of three on this side of the home. In total this home had five, all with peeling paint and wood decay.
The problem began before paint was even applied to the wood. The clapboards were installed right against the roof shingles. Ideally there should be a gap left between the wood and the roof. When the paint was applied the section of wood against the roof never received primer or paint.
Bare wood does not do well exposed to the elements. In addition that is the end grain of the clapboard wood. End grain sucks up water like a sponge. Repeatedly wet wood starts paint to peeling. Next comes the decay. The trim detail in the lower picture shows that a good amount of rot exists on these boards.
There is no secret to painting and protecting wood. Leave room for the wood to breath. Prep ALL sides of the wood, then prime and paint. Repeat as necessary.