"Unless a man undertakes more than he possibly can do, he will never do all that he can." Henry Drummond (1851-1897) Scottish theologist and scientist.
One of the basic concepts of goal setting is to set oneor two BHAG targets. A BHAG is a Big Hairy Audacious Goal. A BHAG would be to grow sales at double your historic rate, to reduce set up on a machine by fifty percent or to land the top five large prospects in the coming quarter. These are goals that are not easy to hit - they are stretch goals.
Jim Collins in his book Good to Great discusses in detail the BHAG.
The reason for pursuing a goal like this is to stretch your mind and your abilities. When the human mind begins to see a goal like this, the first reaction is to reject it as unattainable. After the subconscious mind spends some time processing the goal, it begins finding little ways to get the goal accomplished. Then after a few brainstorming sessions and some back and forth with people that share your vision, the goal can be attacked.
Some believe it's better to plan for 5% growth and hit 5%. Others believe it's better to plan for 20% growth and hit 14%. Without a BHAG you are almost guaranteed to be in the 5% or less range.