It's only when you're told that you're going to be working on this problem, and then you start procrastinating, but the task is still active in the back of your mind, that you start to incubate.
Tek kad ti kažu da ćeš raditi na tom zadatku, i onda počneš prokrastinirati, ali još uvijek imaš zadatak na pameti, tek tada počneš promišljati.