Sea levels rise and fall and many early villages that were once on the beach are now submerged. In the past, people travelled and traded along rivers and lakeshores so traces of those people's activities are often left behind. Sometimes sites are ruined by people who remove the artifacts or damage the site. When people remove artifacts they take away important information - information that can tell us about the people who left those artifacts behind. Archaeologists seek knowledge, not treasure.
Every artifact is a messenger from the past.
Where the object is found and how it fits in with other features and objects at the site is just as important as the object itself. Please take a picture, not a souvenir. Everyone is responsible for respecting and preserving archaeological sites.