Extensive psychological and neuroimaging evidence demonstrates that internal forward models in the brain generate predictive signals about self-produced movements, which attenuate somatosensory feedback and prevent humans from successfully tickling themselves.
The claim is a specific and empirically testable proposition about motor control and somatosensory perception. Multiple highly cited papers and fMRI studies consistently support the forward-model/efference-copy theory of sensory attenuation as the underlying mechanism preventing self-tickling, with no papers refuting this core phenomenon.