Three symbols in "The Lottery" that show the dangers of following tradition are the piles of stones the boys gather, the black box, and Old Man Warner.
The dangers of following tradition are shown in the way children at a young age learn that barbarous rituals are completely normal. For the children, stoning a fellow member of the community to death is presented as just another part of life, hardly different from an annual fair or a carnival. When children are indoctrinated into an unhealthy practice at a young age, it becomes all the more difficult to dislodge it.
The black box also shows the dangers of tradition. The box has clearly outlived its usefulness, just as the stoning has. The box is splintered, fading, and in need of replacement, just as the stoning is, but it is too easy to keep on with what has always been done. People try to ignore the box and all it means rather than facing the hard questions it presents. The box is a chief symbol of how facing change can be kicked downfield like a can but not addressed while severe and unnecessary damage is being done.
Finally, Old Man Warner shows the dangers of being so set in one's ways that one's attitude blocks change. Old Man Warner learned at some point that giving up the ritual of human sacrifice would lead the village backward, to "eating stewed chickweed and acorns," a ludicrous proposition. Nevertheless, his assurance stifles needed change and makes it all the harder for people like the Adams to dissent.