实际发展水平与潜在发展水平之间的距离，前者由独立解决问题决定，后者由在成人指导下或与更有能力的同伴合作解决问题决定。

The night is a great cathedral, but the stars are its windows.

Don't let yesterday take up too much of today.

Happiness in this world, when it comes, comes incidentally. Make it the objet of pursuit, and it leads us a wild-goose chase, and is never attained. Follow some other object, and very possibly we may find that we have cought happiness without dreaming of it.

The darker the past, the brighter the future.

生活是不公平的，习惯就好。