This text explores the concept of the "mental milieu" (osvětí), derived from the ethological term Umwelt. The author likens human thinking to movement within a specific internal environment where an individual must feel "at home," much like a fish in an aquarium. This mental milieu is shaped by language and established mental models that provide a sense of familiarity and stability. Although we are influenced by these structures, the author emphasizes the existence of freedom and will, allowing us to choose the direction of our thoughts and their mutual contexts. The fundamental difference between a physical and a mental environment lies in the nature of their boundaries. While leaving an aquarium is fatal for a fish, for a thinking person, transcending the limits of their current milieu represents an opportunity for a new and remarkable beginning. Overcoming habitual thought patterns thus opens up space for truly innovative thinking and the expansion of intellectual horizons beyond the previously known world.