Stuttering can become very severe if you are in big tension and don't know what to do immediately. If the bus you are planning to board in leaving in next 20 mins and the queue of people standing in line to get tickets in so long , heart beats so much for stutterers and when their turn in about to come to tell the counter guy ,the place of destination where to go, stuttering person will get peak tension. It's all common for stutterers in real life and they plan alternatives to avoid such situations. In the worst case, it's brutal. Its better to write in paper and be prepared and show to the counter guy or anyone if words won't come out. These things likely happen in their nervous 20s and once they reach 40s ,they don't care and they stutter and tell the word openly.