The pain and suffering tag is for posts which discuss ways to measure these phenomena, or issues that are notable for causing especially intense pain and suffering (even if they aren't especially large in scale).
Given that EA tends to focus on the number of people affected by a problem, we may not notice when a problem affects relatively few people but is extremely bad for those it affects, leading to high overall impact. Posts with this tag may push against this tendency.
Content note: Posts with this tag may contain disconcerting or frightening content.