A butterfly, fluttering its
wings in Amazons, can affect
the clouds in China. It means,
every little thing, affects
every little thing in the
universe, in the cosmos. So,
yagnas are those ancient rituals
or practices that have an effect
on the environment, on the
collective consciousness, and
on the individual mind.

http://www.artofliving.org/in-en/what-sri-sri-said-today