Applies particularly well to various situations both realistic and hypothetical. The basic concept being that, a heroin addict will take a hit. He will then enjoy the high while it lasts and then come down, returning to the misery that is real life. Then, there is a period of revoltion, during which he swears he'll never do it again. But, it happens. Slowly, the addiction screams to life and burns the mind. To illustrate, a passage from Trainspotting by Irvine Welsh:

Ah git up fir ma tea, frail, bent and brittle as ah struggle doon the stairs. Every move makes ma blood soar tae ma throbbing heid. At one stage ah thought it wid just burst open, like a balloon, sending blood, skill fragments and grey matter splattering oantae Ma's cream woodchip.

And he goes back, and it happens again. And again. Things that this cycle illustrates particularly well: Abusive sexual relationships, masturbation, alcoholism, school, etc. Subtle, but applies to a lot of things, mainly due to the cyclic nature of everything.