When they've hit the wall.

Here's some sound advice on dealing with this dilemma:

Tip #1: Plan ahead. When you plan ahead and expect that the wall is probably just around the corner, you'll have much more stamina to push through. Preparation proceeds power, so go into this with your eyes wide open--prepared to face the wall of fatigue that you'll eventually run into.

Tip #2: Pace yourself. So often, eager entrepreneurs are in such a rush. What's the hurry? If you give yourself a longer timeline to accomplish your goals you'll enjoy the journey much more. You'll also get a lot further along before you hit the wall, and that realization will give you more motivation to keep on going.

Tip #3: Follow someone's lead and benefit from their draft. You see cyclists do it all the time--by riding about ½ inch from the wheel in front of them they cut headwind resistance by more than 50%. Go get someone with strength and experience out in front of you to show you the way and to lighten the load...this way, you might never even realize you busted right through that wall without missing a beat.