The phenomenological Bose-gas picture rendered no quantitative account for the critical parameters of conventional low-temperature superconductors. Its failure stemmed from the very large diameter ξ of pairs in conventional superconductors which can be estimated using the uncertainty principle, ξ ≈ 1/δk. The uncertainty in the momentum 8k is estimated using the uncertainty in the kinetic energy δE ≃ v F δk, which should be of the order of T C, the only characteristic energy of the superconducting state. Therefore, ξ ≈ v F/ Tc turns out to be about 1 µm for simple superconducting metals where Tc ≃ 1 K and the Fermi velocity v F ≃ 108 cm s−1. This means that pairs in conventional superconductors strongly overlap and the Ogg–Shafroth model of real space pairs cannot be applied.