Must every scene must be different?

This is, of course, a trick question. The answer itself isn't the important part - the important part is that your readers will notice sameness when they encounter it, and expect it to mean something. Which in turn means that if you don't want the sameness to mean something, you have to work towards making every scene different.

Let's get a bit more concrete about when sameness means something.

Let's say you're starting your story with your main character walking into a confrontation with a parent, and the main point of the story is a change in the relationship of that character with the parent. Then it makes sense to put in a scene at the end where there's another confrontation between the character and the parent, and it comes out differently. The repetition is noticeable, and it means something: it means the character has changed, allowing a different outcome from a very similar situation.

In The Princess Bride, we see repetition between the scene when Buttercup first gets introduced to her people as a princess, coming out on the red carpet, and the scene where she walks out with the queen's crown on ("at noon she met her subjects again, this time as their queen...") and gets booed. In the first instance, she's detached but accepting of the situation. In the second, she has her detachment and her acceptance called into question. It creates a terrific contrast, and that second scene had me going "No, no, no!" the first time I saw it. (And it has the boy doing the same thing.)

In The Lord of the Rings there is a repetition of the scene inside Mount Doom - between Elrond and Isildur in the first instance, and between Sam and Frodo in the second instance. Part of the power of the repetition comes in our desire for all the adventures to have changed things and made the situation different, so that Frodo won't fall into the same trap - and yet he does.

In a situation where two scenes are noticeably the same, readers will conclude that any differences they can find will be seriously significant to the story.

Now let's talk about when it's important to make every scene different.

Take my novel in progress as an example. I have a society going where the nobles get messages via servants, and in which the sending of messages is quite common and sometimes quite important. Naturally, this means I have a lot of scenes where servants are delivering messages. The danger here is that there would be too much similarity between the scenes of message delivery - causing people to invest significance in differences between the scenes that really have no particular import. Then of course as we go on and there are more instances of message delivery, it could get extremely repetitive.

In this kind of situation I pay very close attention to which aspects of the scene are important. Is the location where the message is received important? Is the method of delivery (paper or recitation) important? Is the content of the message important? Is the character's reaction to receiving the message important? When I write the scene, the important elements need to stay, but those of less importance can just be skipped. So when Tagret gets a message too sensitive to be written down, he gets it in his own room via recitation - and I make sure to show that. When another message comes and the deliverer wants to be anonymous, Tagret gets a piece of paper slipped under his door. When the message is too urgent to let the family enter the house and relax before receiving it, I have the First Houseman meet them in the entry vestibule to deliver the message. But when Tagret gets the message that a close friend has survived the threat of death, it's not the method of delivery that's important, but Tagret's reaction - so I skip the message delivery entirely and go straight to Tagret's post-message emotions and actions.

Watch out for small details that can become repetitive when you're not paying attention, such as the way you have people respond to danger, or the way they approach doors. If you're always describing these the same way, you're giving your character a habit - which may be charming and work great, or which could be entirely distracting from the conflicts of the story.

The other place where sameness can cause trouble is in larger, more important events. Maybe you're writing a book where a politician is trying to get something done and has to give a number of important speeches. It could turn out to be really awful if everything surrounding those speeches is the same, especially if your politician is giving the speeches about the same topic, just to different people. In that case, it's worth working hard to create different contexts for the similar events.

In my novel in progress, there is a point when the story events start being organized around a political process called Heir Selection. In my Varin world, twelve candidates compete in several rounds of voting so that one can be selected as heir to the throne. The votes are all cast by the members of the Eminence's cabinet. We start with the Round of Twelve, then three days later is the Round of Eight, three days after that the Round of Four, and three days after that the final round. I think you can see the trap. If these events are not to become very repetitive and boring, they must be very different from one another. They must take place in different locations, the type of test put to the candidates must be different, etc. - but even that is not quite enough. I've also found that I have to make sure that I use different points of view, and even take focus off the content of the event. The Round of Twelve is handled in the point of view of one of the candidates on the stage in the Hall of the Eminence; the Round of Eight is outside in the Plaza of Varin, and the questioning that the candidates have been subjected to is not even part of the event.  While the Eminence announces the results of the question session and introduces the four candidates who will be moving on, I stay in the point of view of an audience member who doesn't care at all about what the Eminence says because he's busy trying to stop one of the candidates from being assassinated. My sense is that for the Round of Four I'll be back in my candidate's viewpoint, because this is a spot where his actions during the competition are absolutely critical - but for the final round I suspect the question of the results will be far more important than any character's actions during the ceremonial portion, so the ceremonial part will most likely be omitted.

As I go through this I'm noticing a pattern, which is to say that any time you have repetition it's important to keep the primary focus different. Try to identify what's most important about what is happening, and stick to that. Look around for ways to change setting, character, etc. so you are not simply falling into a reader's comfortable expectations. When their comfortable expectations are being met, readers are far more likely to skim or skip. It's the focus on difference that will keep their attention riveted to the page.

It's something to think about.