When spinning for example there is a whole process to go through before the spin is properly developed
but it can happen extremely quickly and you need to experience an unintentional spin entry from a turn to really understand why it is vital to understand and practice the approaching stall recognition and avoidance principles. It is also vital not the scare the student so when and how are important considerations for any individual.
The Pilot's Lounge #131: Spin Training I don't mind scaring instructor students however - if they haven't experienced it by the time they do their instructor training then they will experience it on the spin session that I do with them. It can easily take two rotations for them to stop the gyrations amidst the swearing after realizing that I (playing his student) have suddenly "lost control" - he had seen turns like this many times before and didn't identify the subtle signs of the imminent stall in this situation. Its not in the PPL syllabus. He had seen lots of stalls from straight flight with plenty of time to patter on the symptoms of the approaching stall. He wasn't expecting it as the pre-flight brief only covered normal spin entries and we'd just done lots of those so he was familiar with the normal process to get it into a fully developed spin.
In the debrief I often get "Does that happen often?" and the answer is "Usually only once in your lifetime."