In Ireland, four-leaf clovers are a symbol of good luck. As the old Irish verse says:
One leaf is for fame,
And one is for a faithful lover,
And one is to bring you glorious health,
Are all in the four-leaf clover.
People look for them in the grass, and they won't resist picking a four-leaf clover and carrying it with them for luck and all the good things that it might bring.