This document discusses concepts in medicinal chemistry design and thermodynamics. It begins by outlining some challenges in drug discovery, such as targeting weakly linked disease targets and predicting toxicity. It then discusses molecular design approaches, including controlling compound properties and sampling chemical space. Key concepts discussed include target engagement potential, property-based design to find an optimal "sweet spot", and using thermodynamics and molecular interactions to analyze activity and properties. The document questions the use of rules and guidelines in medicinal chemistry and advocates analyzing data to understand actual trends rather than assuming functional forms. It also discusses issues with ligand efficiency metrics and advocates using residuals to quantify activity compared to observed trends in the data.