Time is like a river, flowing downstream to the future. You’re swimming in the river, and everything you do flows downstream as well, spreading and dissolving in the water. When you poison the world around you - physically or metaphorically - that poison persists, flowing downstream and washing over others in the river. Then they get sick and vomit out their own poisons.
It’s worth remembering there are a lot of people upstream from us, and there’s a lot of residual poison washing over us. However, even though it often seems personal and directed, the poison is just floating in the river and the people who vomited it have no idea nor control over where it goes. When someone poisons your world, they’re likely just uncontrollably vomiting poison they received from someone else, somewhere upstream.
Of course, we don’t have to add our vomitous poison to the river. Our livers - physical and metaphorical - can cleanse the poison. If everyone just managed to cleanse more poison than they added, the river would finally become clean and pure.