Sometimes the first sentence is the most difficult. You need to find the right one, because it drags all the other ones after it; if it is crooked, it may lead the entire bunch astray. But crookedness is relative; it is contextual; time-bound. What is wrong today, is right tomorrow.
When you are looking for the right sentence, you don't want to start with how people in the trains are different at seven and at ten o'clock. Or how suburbs are different. You don't want to marvel how students are able to write good, long essays in barely a week. Or how others - when they have already done two lecture series and only need one or two points to pass the course - fail so miserably that you have to ask if they have even read the book. And then those who have obviously read the book but apparently haven't read the question, because they write seven full pages and only by accident manage to get in there those four lines, which have something to do with what was actually asked.
Games and competitions. Reaching the next level and getting better, beating previous scores. The question of why that can't be transported into real life. If there is any reason why it even should be. People yelling to each other on the streets of Kallio. Picking up my car from the sisters'. Pancakes and apple jam and whipped cream and my poor cat whom I hardly even noticed. Being able to close the curtains and bedroom door, clean bathroom floors and uninterrupted sleep.
Discovering the correct first sentence, because putting it aright afterwards can be an arduous task.