Window frames (especially uPVC or metal) expand and contract with temperature changes. The surrounding wall materials do so at a different rate, leading to hairline cracks over time.

Windows represent a structural "gap" in your wall, making the surrounding area a natural concentration point for stress.

Through the fog pushing into his living room, he saw shapes. They were tall, elongated things, pressing their faces against the glass from the outside —except their outside was his inside.