I recently watched 'Hot Tub Time Machine'. It's a 2010 American comedy film about four men who were bored with their adult lives and travel back to their 1980s teen-hood, courtesy of a time-shifting hot tub. As they went back in time, they had to try to re-enact their activities back then, or else they would face dire consequences back in present time. For e.g., Jacob, the geeky nephew of Adam, might not exist if his mother did not had sexual intercourse by accident.
'Butterfly Effect' is the sensitive dependence on initial conditions; where a small change at one place in a nonlinear system can result in large differences to a later state. On the positive note, the actors made little changes before traveling back to the present. But due to the butterfly effect, they experienced a change of fortunes. For e.g, Adam impressed his random date, April, then. Hence, rather than suffer yet another fall out with another of his girlfriend, the butterfly effect meant that April became his current wife.
The power of the butterfly is small yet significant. Little actions today could be the deal-breaker 10 years down the road. Whilst I might not be conscious of what greatness it might lead to, it does gives me food-for-thought to be careful in my little ways.