For example, if a fly happens to fly by your nose and you swat it away, this will have an effect on everything and everyone in the world. It is scientifically impossible for anything to be totally isolated from this event. As a thought experiment (because in reality this experiment could not be carried out perfectly), imagine two video recordings of the world as it would be with and without this fly flying by. Play the recordings from your view of when you next observe some other people. It is possible that you may not see much difference immediately, but I'd speculate that within seconds or minutes these peoples' conversations are differing, and you would start to see corresponding differences in movement.
How about someone on the other side of the planet? Perhaps in the first few minutes you would not see any noticeable difference, but i'd speculate that within hours you would detect visible differences. These differences would escalate over time and after days, weeks, months, there maybe no relation between the two videos, though there would be some weaving a set plans are carried out (eg catching a flight, attending a meeting), but even these co-incidences would fizzle out with time, even for the most hardened planners.

