Sometimes you need to play your kikashi while you can. But sometimes it is aji keshi or entails a direct loss. One common mistake is to atari a first-line hane when you are going to tenuki.
Here is an example from Rob van Zeijst's column in the Daily Yomiuri Online.
Giving two points komi, Black loses by one point.
But Black's atari at in the first diagram is a mistake. Black can salvage jigo if he does not play atari.
The difference is that Black has not sacrificed a stone in the top right corner. The extra point gives Black a tie.
What about White's earlier atari? Was it a mistake, too?
If White continues to mirror with :
protects the corner. is tesuji. If captures at a, White plays at b.
So White's early atari seems necessary to prepare for the atari with sente when Black cuts. Two similar ataris, one right, one wrong. Go is not a very easy game.