Door opening by itself
A door that opens by itself is most often hanging slightly out of plumb: once the latch lets go, its own weight swings it toward the low side. It is a good moment to ask which way your own habits lean.
What it may mean
A door that opens by itself is usually not being pushed at all. Its frame or hinges sit a fraction out of plumb, so the moment the latch lets go, the door's own weight swings it toward the low side, slowly and always in the same direction. Nobody touched it; it simply went where it leans. People have a lean too. Give most of us a free night or an empty weekend, and we drift the same way every time: toward the couch and the phone, or toward the garden and the long walk. When a door swings open on its own, notice which way it went, and then which way your own free hours tend to go. Folklore filled such doorways with souls and spirits, and the sight still gives plenty of people a chill. You can keep those stories and still check the hinges.
Depending on how you saw it
A door that creaks open at night
A door that eases open in the dark sounds far louder than it would by day, because the rest of the house is silent. The creak is ordinary; the silence makes it big. Which small thing in your life seems loud only because everything around it has gone still?
A cabinet door that will not stay shut
Kitchen cabinet doors pop open when their hinges loosen or the cabinet leans forward a little. Each time you close one, it eases open again. Which small repair have you been putting off because the problem only shows up now and then?
A door opening just as you think of someone
If a door swings open at the very moment someone comes to mind, the timing can seem almost pointed. Coincidences like this stay in memory, while the many times a door moved and nobody was on your mind are forgotten. Who was it, and is there something you would like to tell them?
Why it happens in nature
Doors open on their own when the frame or hinges are slightly out of plumb, so the door's weight swings it toward the low side. Pressure changes from an opened window, an outside door or a furnace fan can push an unlatched door, and wood swells and shrinks with humidity, which changes how well a latch catches.
What folk beliefs say
Germany
German children were taught not to slam doors violently, because the soul of their dear old grandmother might be following them and could be pinched.
Source: Cora Linn Daniels; C. M. Stevans (eds.), Encyclopaedia of Superstitions, Folklore, and the Occult Sciences of the World, vol. 1 (1903), vol. 1, p. 437. View the page
Netherlands
Many old houses in Holland had a special door that was opened only for a marriage or a death: the bride and groom entered through it, and it stayed barred until a coffin had to leave the house.
Source: Cora Linn Daniels; C. M. Stevans (eds.), Encyclopaedia of Superstitions, Folklore, and the Occult Sciences of the World, vol. 1 (1903), vol. 1, p. 437. View the page
Hungary
In Hungary, having trouble turning a door handle was taken as a sign that you had forgotten to say your prayers.
Source: Cora Linn Daniels; C. M. Stevans (eds.), Encyclopaedia of Superstitions, Folklore, and the Occult Sciences of the World, vol. 1 (1903), vol. 1, p. 437. View the page
To reflect on
Which way do you drift when nothing is holding you in place?