Bit rot is a phenomenon where software decays over time due to changes in dependencies and tooling required to build, test, and deploy it. This can happen even if the code hasn't been touched for years, leading to unexpected breaks in functionality. Bit rot occurs because software is built on top of hundreds of different pieces from open source frameworks and libraries, which are updated and patched with varying frequency, sometimes requiring changes that break compatibility with other parts of the application stack. The longer an application has been running, the more susceptible it becomes to bit rot, as dependencies accumulate updates and potential incompatibilities. To combat bit rot, developers can take steps such as keeping dependencies up to date, using lockfiles and container images for reproducibility, minimizing excess dependency usage, writing integration and unit tests, and running tests regularly.