This has probably happened to you at some point while watching a film - you suddenly say "I knew that was going to happen." It just means you're smarter than the writer of that film, I don't mean intellectually; simply that your level of understanding the story is greater than his/her ability of writing it. Predicting a scene just means that you've watched or read so much over the years that you're able to figure out what's going to happen before it actually does - sort of like history repeating itself or a déjà vu moment.
What once worked in a Shakespeare play might not work anymore because the audience can predict what's gonna happen. This has nothing to do with the ability of the writer but our ability of understanding the story. I've been schooled in writing/making films so I know the ins and outs and all the gimmicks that go along with developing a screenplay. The trouble is the audience is also learning all this and getting smarter as years pass (especially with the help of "Making of" featurettes available on DVDs and BluRays).
Very rarely do I find the movie going experience entertaining any more - unless it's a classic I'm watching (for the umpteenth time) chances are I won't like it. Personally, films that I enjoy the most now are ones that entertain in a new way. What I mean by this is... because so many stories have been told over the year it's very difficult to find something original, I mean how many times can we watch a boy meets girl or rich girl poor boy story. No, what I expect now is not an original story but one that's presented in a new way or with a twist on the original.
The trouble is 99% of film makers believe wholeheartedly that they know what the audience wants and thus they keep churning out the same old lame stuff; and then they wonder why their films fail. To these film makers signing a big star guarantees a big opening and recovery of the cost in the first week - the story be damned! But soon they'll realize that this no longer works, films are getting expensive and the first week is not enough to recover the cost. Films have to last for several weeks and must have a good story otherwise why would people pay their hard earned money to go to the movie theater when they can download it within a few days from some pirate website or watch it on TV in a couple of months for free?
The future is very bleak for films even gimmicks like 3D can't save the film industry when there are better stories elsewhere. If films were free people wouldn't care how bad the stories were - this is why TV soaps are so popular - they're inexpensive to watch - you don't have to shell out Rs. 200 per person to watch them. The problem being ignored is that most screenwriters are learning the same style of writing that existed 30, 40 or 50 years ago. If you're a scientist or a medical doctor you're not going to learn methods that were taught 50 years ago, you'll learn the most modern methods. Unfortunately, in Bollywood, there is no real body that exists for teaching how to write screenplays.
Screenplays evolve with the story, a style that works for one story won't necessarily work for another. Writers need to learn that boy meets girl doesn't work because it's predictable the audience already knows they will live happily ever after; what happens in-between doesn't really matter - unless you can present it in a new way - who cares. Until writers learn this and stop being brainwashed into writing the three acts style, films will be predictable and boring and we will witness many more déjà vu moments...