Q+A-Why did North Korea rush to a nuclear test?

Obama is being the tough guy according to Al-Reuters.

North Korea likely concluded that no concessions would flow from U.S. President Barack Obama, especially after his strongly worded response to Pyongyang’s rocket launch last month that regional powers say was a long-range missile test. To North Korea, this probably signalled Washington was in no mood for direct negotiations, something long sought by Pyongyang.