Once one has learned to hane at the head of two stones, it becomes a natural instinct to do it even when you have only one supporting stone instead of two. This seems to be a common problem around the 10k level.
If Black has a stone at x, is excellent shape. But without that
stone, he is asking for a fight in a situation where he is weaker. He
has played into an atekomi and the cutting point at a is crying
out to be exploited.
It is quite possible for to be a fine move for tactical reasons based on
nearby stones, but it should generally not be your first instinct.
This is the standard response to (which in turn is the standard
response to the shoulder hit of Black's first stone). Black's and
White's groups are now equally strong, with the same number of
liberties.
Author: Dan. I am only 5k, so comments and corrections are most welcome!