Ionization potential depression (IPD) is of crucial importance to understand and accurately predict the properties of dense partially ionized plasmas. Many models of IPD have been developed that, however, exhibit largely varying results. Recently, a novel approach was proposed that is based on first-principles quantum Monte Carlo simulations and that was demonstrated for hydrogen [Bonitz \textit{et al.}, Phys. Plasmas (2024)]. Here this concept is discussed in more detail. Particular attention is devoted to the Fermi barrier that electrons have to overcome upon ionization and which significantly contributes to IPD when the nuclear charge increases.