Consider the illustration to the left, and imagine a hypothetical discount offer to prevent customers from churning. On the left we see what would happen if a given customer wasn't treated, and on the right, what would happen if they were treated.
We want to avoid the harmful scenario, namely where we treat a user who churns if treated, but would have remained if left untreated. This is a very real risk since even a good discount can often remind a customer to churn. Ideally a retention campaign would only target the desirable scenario, where the user remains because of the offer.