Through the process of imperceptible gradual change, innocent carefree kids grow up into ambitious youths, generous chivalrous youths mature into unfeeling grownups, vigorous aggressive grownups deteriorate into mulish old fogeys.
Since the change takes place by slow degrees---year by year, month by month, day by day, hour by hour, minute by minute, second by second, you feel as if you were permanently your same old self always seeing much fun and meaning in life, like one, walking a long, long way down an extremely gentle mountain slope, hardly perceives its degree of incline or notices the altered scenes as he moves along. You thus take a positive view of life and find it endurable.