The Allegory of the Cave. The dialogue between Socrates and Glaucon is probably fictitious and composed by Plato; whether or not the allegory originated with Socrates, or if Plato is using his mentor as a stand-in for his own idea, is unclear. In the dialogue, Socrates asks Glaucon to imagine a cave, in which prisoners are kept.
The d sublevel consists of five orbitals that can hold a maximum of  two electrons each. The total maximum number of electrons that the  d sublevel can hold is 10 electrons.
Since any orbital can hold a maximum of two electrons, the bonding orbital in H 2 + is only half-full. This single electron is nevertheless enough to lower the potential energy of one mole of hydrogen nuclei pairs by 270 kJ quite enough to make them stick together and behave like a distinct molecular species.