Most of the previous answers are pretty much on target.
I'm going to expand a little on something other readers already talked about. Sometimes there is a big change going on inside us that our mind, up on the surface, know nothing about. It could be physical, like an actual pregnancy, but it could also be another type of change, a spiritual one, or emotional, or whatever.
When, after sitting under the bodhi tree, Shakyamuni Buddha achieved enlightenment, that was only possible because he had been pregnant with it for years, and only then gave birth to it. Before that, he had had what seemed to be a perfect life --a prince, with riches, power, a wife and son he loved-- not to mention the sort of life he was expected to have as a member of the Kshatrya caste. And all of a sudden he left all of that behind, and never looked back. That looks like a rash, impulsive decision, but was anything but --he had been pregnant with it for a while.
I'm using a story like Buddha's because it's easy to see the patterns there, but we have all encountered in our personal lives examples of those sudden, radical changes that only seem to come out of nowhere, or have even experienced them ourselves...