• Imperfections of planning domain models
• Incomplete models
• Incorrect models
• Inadequate models
• Intractable models
• Learning from the environment
• Learning by experimentation (EXPO)
• acquiring new preconditions
• acquiring new effects
• Reinforcement learning
• Q-learning

Gil, Y., "Learning by Experimentation: Incremental Refinement of Incomplete Planning Domains", Proceedings of the Eleventh International Conference on Machine Learning (ICML-94). (pdf file)

Sutton, R. "Integrated Architectures for Learning, Planning, and Reacting based on Approximating Dynamic Programming". Proceedings of the Seventh International Conference on Machine Learning (ICML-90).