Human developmental periods
Development occurs in successive phases. Its course depends on the experience previously acquired by the individual. In each phase, a new system of biological, social, psychological obstacles emerge, causing crisis and exacerbating the struggle between the aspirations for progression and regression. To move to the next phase, all obstacles must be overcome. The solution to a psychosocial crisis occurs when the obstacles and pressures that have arisen at a given moment are incorporated into the structure of the ego as elements of a harmonious whole. Then the relative equilibrium is not so much recovered as achieved at a higher level of complexity.