In Ways of Seeing, John Berger answers:
When in love, the sight of the beloved has a completeness which no words and no embrace can match: a completeness which only the act of making love can temporarily accommodate.
I also thought of knocking on the door of our old house, explaining that I was born there, that I lived there until I was eleven, and wanted to look around. I abandoned the idea as soon as I’d thought of it. Houses have no loyalty. We can live in a place ten years and within a fortnight of moving out it is as if we have never been there. It may still bear the scars of our occupancy, of our botched attempts at DIY, but it vacates itself of our memory as soon as the new people move their stuff in. We want houses to reciprocate our feelings of loss but, like the rectangle of unfaded paint where a favourite mirror once hung, they give us nothing to reflect upon. Often in films someone goes to a house where he once spent happier times and, slowly, the screen is filled with laughing. This convention works so powerfully precisely because, in life, it is not like that. It testifies to the strength of our longing: we want houses to be haunted. They never are.
In The Selfish Gene, Richard Dawkins answers:
A stable thing is a collection of atoms that is permanent enough or common enough to deserve a name. It may be a unique collection of atoms, such as the Matterhorn, that lasts long enough to be worth naming. Or it may be a class of entities, such as rain drops, that come into existence at a sufficiently high rate to deserve a collective name, even if any one of them is short-lived. The things that we see around us, and which we think of as needing explanation—rocks, galaxies, ocean waves—are all, to a greater or lesser extent, stable patterns of atoms. Soap bubbles tend to be spherical because this is a stable configuration of thin films filled with gas. In a spacecraft, water is also stable in spherical globules, but on earth, where there is gravity, the stable surface for standing water is flat and horizontal. Salt crystals tend to be cubes because this is a stable way of packing sodium and chloride ions together. In the sun the simplest atoms of all, hydrogen atoms, are fusing to form helium atoms, because in the conditions that prevail there the helium configuration is more stable. Other even more complex atoms are being formed in stars all over the universe, ever since soon after the ‘big bang’ which, according to the prevailing theory, initiated the universe. This is originally where the elements on our world came from.