Together with testing, analog contact tracing, and digital contact tracing, protection of those in isolation and quarantine – legally, socially, and economically – is an essential component of the Test-trace-isolate-quarantine (TTIQ). Without this fourth pillar, the other three will not function. A TTIQ strategy requires altruism, which should be facilitated and recognized. It also requires great clarity on who pays for testing, contact tracing, isolation, and quarantine, what happens to those identified as ill or as contacts, the reasons for policy choices including the trade-offs involved and why chosen policies fulfill the subsidiarity requirement, and the status of digital proximity tracing. Cooperation with the strategy must be made easy for populations with very different pressures and needs; its success therefore depends on our ability to clarify relevant information to all of these populations, and to make cooperation feasible for all of them as well.