The word "Chai" appears in the popular Hebrew slogan "Am Yisrael Chai!" (עַם יִשְׂרָאֵל חַי - "The people of Israel live!"
It is believed that the envious glare of onlookers, even without any ill intentions, can cause divine repercussions. it could also be considered helpful to wear or display such an amulet from a totally practical point of view - simply to consistently remind oneself of our own fragility and weaknesses, and to help us reflect this realization in our day to day thoughts, speech and actions.