The DevTeam Thinks of Everything
The DevTeam Thinks Of Everything, abbreviated as TDTTOE, is a term used to describe when the NetHack DevTeam anticipated the player getting into an unusual situation, and programmed in special behavior for that case. This means that if you think of doing something "clever" in the game, the DevTeam most likely thought of it too, and the game will produce a realistic but unexpected response.
One prominent example is seen when attempting to #dip a potion into itself:
This is a potion bottle, not a Klein Bottle!
Or, similarly, placing a bag inside itself:
That would be an interesting topological exercise.
Or you might speculate that you might be able to cure your blindness by applying and removing a blindfold, but
You were wearing a blindfold. You still cannot see.
Or you might know that tip is designed for spilling items out of containers, but decide to try tipping your fedora:
You briefly doff your fedora.
As a far more complex example, upon #praying to your god when he/she is sufficiently angry, you may receive the following from your god:
Thou hast angered me.
This is followed by a (usually) fatal bolt of lightning striking you from the heavens. However, with shock resistance, the attack can be survived. This is then repeated with a wide-angle disintegration beam, but with disintegration resistance, this can also be survived. If this occurs, then:
You bask in its black glow for a minute... [Your god] says: "I believe it not!"
Obviously, this example has much more effect on the actual gameplay than the previous trivial messages.
This is a trope on TVTropes. Originally, the trope was named "The DevTeam Thinks Of Everything" based on NetHack, but then got changed to "Developers' Foresight" because its editors were misusing it as "The DevTeam Thinks Of Something Cool".