Why did Rutherford know that his model would need to be modified right away?

Rutherford knew his atomic model would need modification because, although it successfully described the nucleus and its positive charge, it could not explain the stability of atoms or the observed spectral lines of elements. His model suggested that electrons orbiting the nucleus would lose energy and spiral inward, ultimately leading to atomic collapse, which contradicted the stability of matter. Additionally, the lack of a mechanism to account for electron arrangements and energy levels indicated that a more complex model was necessary.