An interesting concept came up in chess study yesterday: the idea that a knight cannot lose a tempo. This is an important concept in the study of endgames. But this characteristic of the knight is really derived from a simpler characteristic: the knight always alternates the color of its square on every move.
Do you see a solution? There are many, but the idea to take away is that the bishop simply needs to waste time (lose a tempo) to let Black move his king to the h8 square, and then White can deliver the check on the next move. So play might go 1.Bd2 Kh8 2.Bc3+.
Now try the same position a different way. The new restriction is that you may only move the knight.
When you are tired of trying, look below the fold for the answer.
Stumped? That's just it! The knight is on the wrong color square to deliver a check. On each move both the White knight and the Black king will change their square colors, so a check still isn't possible. What White needs to do is make some kind of waiting move to lose a tempo. But try as you might, you just can't find a way to do this using just the knight. And all because a knight cannot lose a tempo. Sometimes there's just never enough time for a knight.