Please explain

In all the cases where β⁺ decay is allowed energetically (and the proton is a part of a nucleus with electron shells), it is accompanied by the electron capture process, when an atomic electron is captured by a nucleus with the emission of a neutrino:

energy

+

p+

+

e−

→

n0

+

νe

But if the energy difference between initial and final states is low (less than 2m_ec²), then β⁺ decay is not energetically possible, and electron capture is the sole decay mode.