This is another little paragraph of The Man Who Was Thursday from GK Chesterton that I went back in search of:
In that place they dined and slept, both very thoroughly. The beans and bacon, which these unaccountable people cooked well, the astonishing emergence of Burgundy from their cellars, crowned Syme’s sense of a new comradeship and comfort. Through all this ordeal his root horror had been isolation, and there are no words to express the abyss between isolation and having one ally. It may be conceded to the mathematicians that four is twice two. But two is not twice one; two is two thousand times one. That is why, in spite of a hundred disadvantages, the world will always return to monogamy.
So true it is that the magnitude of difference between doing a thing alone and doing it with one other is immense, as is the difference between being alone against the world and having one other on your side.