How many failures does each success require?
Think about it, if it was possible to do it best the first time around, we would do everything once and retire. No, from the top to the bottom of achievements there are failures on the road to success. It may be relatively "easy" to climb Mt. Everest today using oxygen and Sherpas, but even today, almost every year a Sherpa dies in the ice fall. A failure for others success. Tumblr was just bought for over a billion dollars, how many other blogging platforms will never be anywhere near that size? For every runner on the starting line of the Olympic Trials there are two or three others that trained hard and put in far more effort than most people understand and yet aren't even at the Trials.
Because I am analytical here are some actual numbers, the Everest total success ratio is 29.44%. Roughly 10-15% of people that run under 2:30 in the United States (550-700 performance every year) end up running at the Olympic Trials. The first rocket the US wanted to send astronauts up on, I don't believe it was Redstone but that program did have 5 successes and 1 failure, had only an 80% success ratio, not good enough for human spaceflight.
The point of all this is that sometimes you will fail. In business I am zero for four attempts (RIC, I-Beam Ice Axe, my unemployment book, and the hangboard). Yet in every failure there are lessons to be learned (advertising, patience and market research, persistence, and advertising respectively). In other words, don't be afraid to fail, because you will fail along the way anyway. Since 2010 my summit to attempt ratio for climbs and mountains is around 20%, because I picked the hard way. Not every climber as weak as me tries to solo the Nose on El Capitan.
Epilogue: Why am I writing this now? Because I am beginning to prepare for an October marathon, and I really want to run 2:17. The problem is that is somewhat better than any other race I have ever run. Going after that goal is almost certainly the way to fail. However, I don't want to run a 2:28 or 2:26. I don't have to actually decided on my goal pace until September, so it's base building time. I have a lot of work to do.