Sacrifices may be performed on a regular basis, according to established patterns of daily, monthly, or seasonal acts, or on special occasions, notably at important times in an individual's life (birth, puberty, marriage, death), and in the face of extraordinary conditions. The purpose of the act is either to establish or sustain a proper relationship with the god or gods. Sacrifices may simply express homage and veneration, or they may give thanks for good fortune. Sacrifices of supplication are intended to provoke good fortune, and sacrifices of expiation are offered to appease the divine wrath kindled by humanity's transgression of other arrangements. Humans have been known to sacrifice anything that they have ever used or produced; the oblation may be left exposed; poured, if liquid, into the ground; or burned.