The ability to interact with and modify a running program is one of the great strengths of modern programming languages. But runtime modification forces us to make trade-offs at every stage of a program's design. After several years of work on tools to mitigate this problem - Lazytest, tools.namespace, Component, the 'reloaded' pattern - this is the story of what I've learned, mistakes I made, and the problems that still need to be solved.