Concerns about the trustworthiness of science are not confined to fringe groups that reject science entirely. There is substantial unease even among researchers about the reliability of peer review and the reproducibility crisis---where scientific results are not or cannot be tested by replication. Here the authors point out that such worries even apply to mathematics---for many the language of science. This is largely caused by the growing complexity of our knowledge base, where results are more complicated and investigators sometimes have to rely on the results of others that they do not fully understand. This means, as with the sciences, mathematical discoveries increasingly have to be treated as not absolutely reliable, but as part of a process of searching for the truth, and even what it means for something to true.