The fact that we cannot perceive the curvature of the Earth with our own eyes from ground level is not a flaw in the theory of a spherical Earth, but rather a consequence of the Earth's large size relative to our observation point and the limitations of human perception.
The Earth has a circumference of approximately 40,075 kilometers (24,901 miles), and its curvature is quite gradual. From our everyday perspective at ground level, the Earth's curvature is not readily apparent due to its vast size. Imagine standing on a large field or near a body of water—over short distances, the surface appears flat, even though it is part of a curved surface.
To observe the curvature directly, you would need to be at a significantly higher altitude or in space. Astronauts aboard the International Space Station, for example, can clearly see the curvature of the Earth because they are far above its surface. Similarly, when viewing the Earth from high-altitude locations like the top of a mountain or in an airplane at cruising altitude, you can start to notice the curvature, especially over long distances or when comparing the horizon to distant landmarks.
Additionally, there is plenty of scientific evidence supporting the spherical shape of the Earth, such as satellite images, photographs taken from space, the ability to circumnavigate the globe, and the phenomenon of ships disappearing hull-first over the horizon.
In conclusion, while we cannot directly perceive the curvature of the Earth from ground level, it is not a flaw in the theory of a spherical Earth. The curvature becomes more evident when viewed from higher altitudes or through other means of observation.