Suppose that the early Universe starts with a quantum spacetime originated cosmological $Lambda$-term at the Planck scale $M_{rm pl}$. The cosmological energy density $rho_{_{_Lambda}}$ drives inflation and simultaneously reduces its value to create the matter-energy density $rho_{_{_M}}$ via the continuous pair productions of massive fermions and antifermions. The decreasing $rho_{_{_Lambda}}$ and increasing $rho_{_{_M}}$, in turn, slows down the inflation to its end when the pair production rate $Gamma_M$ is larger than the Hubble rate $H$. The density $rho_{_{_Lambda}}$ and Hubble rate $H$ are uniquely determined by two independent equations from the Einstein equation and energy conservation law, besides the $rho_{_{_M}}$ is determined by pair productions. As a result, inflation naturally appears and theoretical results agree with Planck 2018 observations. Suppose that the reheating efficiently converts $rho_{_{_Lambda}}$ to $rho_{_{_M}}gg rho_{_{_Lambda}}$ accounting for the most relevant Universe mass, and some massive pairs decay to relativistic particles of energy density $rho_{_{_R}}$ starting the hot Big Bang. The back reaction $rho_{_{_M}}leftrightarrow Hleftrightarrow rho_{_{_Lambda}}$ is weak but continues. As a consequence, $rho_{_Lambda}$ closely tracks down $rho_{_R}$ from the reheating end up to the radiation-matter equilibrium, then it varies very slowly, $rho_{_Lambda}propto$ constant, due to the transition from radiation dominant epoch to matter dominant epoch. Therefore the cosmic coincidence problem can be possibly avoided.
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