Quantum gravity thought experiments, such as the firewall paradox, probe the compatibility of quantum theory with general relativity. The usual conclusions of these experiments rely on the universality of quantum theory—the assumption that we can always apply the theory to any physical system, including black holes. Similarly, non-gravitational thought experiments from quantum foundations, like Wigner’s friend paradox, also rely on the universality assumption. They examine scenarios involving multiple physicists, each applying quantum theory to different physical systems, which may themselves consist of other physicists. A key lesson learnt from these thought experiments is that combining the different physicists’ perspectives is far from straightforward. Even a seemingly intuitive rule—that if physicist Alice knows that physicist Bob knows a measurement yielded result x then Alice also knows this measurement has result x—leads to contradictions. In this chapter, we revisit quantum gravity thought experiments like the firewall paradox and point out that they also crucially depend on such combination rules, some of which have been implicit so far. They can, therefore, be understood as gravitational versions of Wigner’s friend thought experiments. This correspondence enables the transfer of insights between quantum foundations and gravity. In particular, the lesson from quantum foundations—that the universality of quantum theory conflicts with seemingly self-evident rules physicists use to combine their perspectives—applies equally to the firewall paradox. Questioning the validity of these rules thus offers a new avenue for resolving it.