Analysis of demographic data on human mortality and lifespan carried out according to the com plete Gompertz-Makeham model μ = C + λe γxt shows that, over the last 100 years, the life expectancy increased almost exclusively because the Makeham parameter C decreased. The observed changes in the demographic aging rate γ and in the initial vitality, which is inversely proportional to lnλ, may be largely an artifact of the attempts to decompose mortality data related to conditions that significantly change within a time scale comparable to the human lifespan, whereas the correct decomposition of mortality change by dif ferent Gompertz-Makeham parameters is possible only for a strictly homogeneous population under strictly stationary conditions. What actually remains of changes in these parameters, while theoretically significant, would probably be negligible in the quantitative practical aspect. The comparison of this situation with exper iments on animals, suggesting possible interferences that may decrease the aging rate and/or increase the lifespan, reveals that the main factors of reduced mortality and, correspondingly, increased lifespan in human beings are limited to one's personal commitment to following long standing and readily available guidelines for healthy life, which may help bring one's lifespan about 10 years closer to the reliably recorded maximum of 122 years, although they obviously do not guarantee it. The bottleneck for the realization of this reserve resides in public and individual mentality rather than in science.