"It means never try to catch the very top (the last thrust in a bull market, when conditions tell you it's too risky; i.e., when momentum, emotion and stimulus [but not fundamentals] are pushing the market higher), and never wait for the perfect bottom (when stocks, because of momentum and fear, are moving lower past the point where conditions tell you it's time to reengage)."As for the perils of trying to catch “first eighth”, that would be jumping on board during the first up move after a steep decline, without general conditions signaling you do so; the term is “whipsaw”, and it’s an ugly thing to experience.
"One of the most helpful things that anybody can learn is to give up trying to catch the last eighth—or the first. These two are the most expensive eighths in the world. They have cost stock traders, in the aggregate, enough millions of dollars to build a concrete highway across the continent."