Above all, never think you're not good enough. Never think that. In life people will take you at your own reckoning. - Isaac Asimov

Very few people are aware of the fact that in the beginning the proud and glorious phrase "dirty old man" was actually meant as derision.
The very phrase, originated as it was by young men, is a standing testimonial to the ignorance of the same young men. Sex is dirty — if you do it right. Young men don't know how to do it right, so they stay clean. Some old men never learn how and they stay clean, too.
But unless you have the ambition to retreat into dull hopelessness, don't you do it. Don't be bashful with ladies while young and retreat altogether as you grow older. Grow bolder with the years: advance, advance.
Be a dirty old man and be proud of it.

Control of self and society has been left to chance or to the vague gropings of intuitive ethical systems based on inspiration and emotion.

To anyone who has been in space and experienced its changelessness, the real excitement of space flight comes when it is time to land on a new planet. The ground speeds backward under you as you catch glimpses of land and water, of geometrical areas and lines that might represent fields and roads. You become aware of the green of growing things, the gray of concrete, the brown of bare ground, the white of snow. Most of all, there is the excitement of populated conglomerates; cities which, on each world, have their own characteristic geometry and architectural variants.