Languages with multiple paradigms or other special-purpose features often are implemented in ways that make true concurrency difficult in the virtual machine or runtime system. Several popular languages feature a global interpreter lock that limits them to pseudo-concurrency. This talk presents lessons learned in developing true concurrency for a goal-directed, object-oriented language called Unicon. Parts of the work were anticipated, such as switching to thread-safe C library functions, while other parts were a surprise, such as eliminating race conditions in self-modifying virtual machine instructions.