In cosmology, the cosmic curvature K and the cosmological constant are two most important parameters, whose values have a strong influence on the behavior of the universe. Under the assumptions of positive energy density and negative initial pressure, by analyzing the dynamic relationship between cosmological variables and parameters, we find that the initial singularity of the universe is unreachable, and K=1,0≤Λ<10-24ly-2 . This means that the initial Big Bang may be impossible at all. The global spatial structure of the universe should be a 3-dimensional sphere S3 . The evolution of the universe should be cyclic, and the cosmological constant should be zero or an infinitesimal. Since the proof is very simple and elementary, and the preconditions are generally accepted facts, these logical conclusions should be quite reliable. Obviously such constraints would be much helpful to correct some popular misconceptions and further discover the properties of dark matter and dark energy in cosmology. In some sense, we restored Heraclitus' ancient faith: “The world, an entity out of everything, was created by neither gods nor men, but was, is and will be eternally living fire, regularly becoming ignited and regularly becoming extinguished.”