Many people find it difficult to get acquainted with strangers. When placed in a situation where they need to work with others, they move to the people they already know. If there isn't anyone in the group with whom they are familiar, they may try to withdraw and not participate in the work that needs to be completed.
Ice breaker activities are designed to be enjoyable, non-threatening activities that allow people to become comfortable with those around them. The activities generally require active involvement and revealing some information about oneself from everyone in the group. As everyone in the group takes part in the activity and learns something about everyone else, the others cease to be "strangers." A perception that the members of the group are acquainted with each other and are able to work together develops and allows for further activities to be undertaken.