The taiji master Zheng Manqing, in his book Thirteen Treatises on T'ai Chi Ch'uan, refers to an ancient saying: 'daily enhancement is measured by the thickness of a sheet of paper.' I first read this sentence when I was a kid, around the time I encountered the old Boy Scout koan: 'How do you eat an elephant? One bite at a time.'
Both these sayings seem pretty negative at first glance. Hard to find something flimsier than a single piece of paper. An elephant is a daunting large meal to eat one bite at a time. But time and determination turn both sayings around. Stack enough pieces of paper together and you have a book. Chomp down on one bite of elephant at a time, and you'll swallow the last bit sooner or later. (If you have a big enough freezer to keep the rest of it fresh.)
The sayings do contain a caution, though. Don't start any big project hoping to finish on day one or two or even thirty. Don't despair when incremental progress seems insignificant compared to the magnitude of the task. Be careful when you try to choke down three or four bites of elephant at a time: they can stick in your throat, and they're awfully chewy.
But if you keep from choking, or from tearing up your daily piece of paper in a fit of frustration, well—eventually you'll have to go looking for a new elephant. Or for a new book to write.