"Santas" are generated by particles of "spirited" matter, known as "elves". "Elves" exists in nearly all lving beings capable of doing good deeds or acts of kindness. As "Santas" are generated, the being feels a sense joy/happiness/jolliness. However, a critcal mass of "elves" must be present to start the energy transformation. Only certain beings have a high concentration of "elves" and can generate the hugh "Santa mass" required. These are the "Santa Claus"s of our legends.
The shorter, colder days of winter and small children act as catalysts for this reaction. These catalysts allow beings with average amounts of "elves" ( less than "Santa mass") to transform a limited amount of "santas".
Unfortunately, anti-santa energy , "humbug", can disrupt the local field affect of "santa" conversion. The origin of "humbug" is unknown but may be related to bad plum pudding and holiday traffic jams. The interaction of high-engery "humbug" and large "santa mass" can lead to the "scrooge cascade". The result of the cascade depends on the quanta of each in the interaction.
Of course, this theory is not restricted to Western cultural legends. As most large populations have similar legends, this must be a universal occurance. Therefore, the Santa Claus story is not so much a fairy tale but a misunderstand of specialized physics.
Susan Shinkai, resident revisionist and idealist, first Christmas Physicist