Have you ever read a book or watched a movie, gotten to the end and been like "Omo mehn, this end no too make ọ," that could be because the payoff did not match the promise.
In the beginning of a book or movie, in the first scene,the first chapter or even before (in the prologue) three types of promises are made, and it is usually a promise of tone, of character and of plot. Every good book/movie has these.
The beginning can show if we are going for a dark tone, a comedic plot or an unreliable narrator kind of thing. You cannot actually give a dark tone in the beginning, come to the end and make it comedic. It leaves the audience feeling cheated. You also cannot create a dark, broody character and make them come off as flippant towards the middle. Even if they change and undergo a character arc, it should be consistent with the promise made in the beginning and the core of the character that and been set up.
I will give more examples when "Nepa" gives me light. Thank you.