This is the tendency for other people’s decisions to affect our decision.
When a group of people is faced with a choice, and they make their decision sequentially, and people making the decision later can see what earlier decision-makes decided, will tend to make the same decision. This is a form of groupthink, social pressure, or a desire to agree.
For example, if a new restaurant opens, we have an implied decision of whether or not to eat there. Everyone else has this same decision. Over time, people decide to eat there. We become aware of these decisions, and it influences our decision of whether or not to eat there.
Colloquially, this is an example of: “Well, everyone else is doing it, so we might as well do it too.”
For a more stark example, say a board needs to vote on an action, and the vote is taken in the open, in sequence: the chairperson goes around the table, asking each board member to say their out loud. By the time the chairperson gets to Member X, that member is aware of all the votes of the people before them. This means Member X is more likely to vote with the group, because the social effect (the information) of those votes has “cascaded” down to them.
The effect is exponential. Someone’s decision can affect multiple other decisions, which then can each affect multiple other decisions, etc.
In another sense this is the scientific phenomenon of “social momentum” or “going viral.” This is one way that information moves through cultures.