Everyone sets goals at one time or another. Some people reach them, others don’t.

A major reason people give up on their goals is that they underestimate the length of time it takes to achieve whatever they are seeking.

Yesterday was the New York Marathon. All the runners in the race understood that it was a 26.2 mile course. Knowing the length of the race is critical. I suspect that a lot fewer runners would have finished (the 26.2 miles) if the organizers had said:

“OK, this is a long race. We are not going to tell you how long. Just go out there and start running. We’ll tell you when you cross the finish line.”

The problem with many of the goals we set is that we don’t know if we are running a 10, 20 or 50 mile race. If we only knew in advance how long we had to run, many more of us could stay the course.

A friend of mine started a business a year ago. It looked terrific on paper, and he had the capital and personnel to pull it off. The darn problem was that he did not know in advance how long it was going to take to get the business into the black. I saw him the other day. He looked tired.

“What have you learned?” I asked.

“That however long you think it is going to take to get a new business profitable, double or triple your estimate,” he suggested.

Fortunately, he is staying with it. Not everyone could.

Having a goal with a discrete time line is very helpful. The problem is that many goals are unmarked time wise. You just have to go out there and do your best every day … then the next, the next and the next. You have to say to yourself: “if I just keep doing those things that are most likely to get me to the finish line, then sooner or later, I will get there.” Sometimes that is easier said than done.

In a powerful illustration of this point, Victor Frankl, who wrote about life in a concentration camp, noted that the great majority of prisoner deaths occurred at the end of the year. Speaking with doctors, he learned that this was not because of harsh weather or other physical conditions. It was because prisoners had told themselves that they would be home by year end, they dreamed that dream and stayed alive with that date in mind. But, when year end came and went, they lost the will to keep going.

I think the best advice for goal setting is what my entrepreneur friend said: “however long you think it is going to take, double your time line.”

Jim Randel is the founder of The Skinny On book series. His latest book, The Skinny on Success, is in stores now.