An impromptu rally usually requires specific circumstances to ensure that the purpose of the rally is clear and meaningful. Here are some possible scenarios: 1. **Emergency social or political issues**: Serious social injustice, policy changes or political events have occurred, and public attention and response are urgently needed. 2. **Emergency**: Natural disasters, accidents or other emergencies require the mobilization of the public to respond quickly to provide support or assistance. 3. **Major community events**: Events in the community require immediate public support, such as protecting public resources or responding to community crises. 4. **Expression of solidarity and solidarity**: Expressing support for an event or group of people requires immediate mobilization of the public to show solidarity. 5. **Exploiting temporary media or public attention**: A "window of opportunity" appears, such as a related large-scale event or media focus, which can be used to attract more attention. 6. **Quick response to influence decision-making**: When decision-makers are about to make important decisions, rallies can be used as a quick mobilization of the public to put pressure on decision-makers. In these cases, organizers need to ensure legal compliance, safety and good organization and management to ensure that the rally can be peaceful and effective.