One fully expects that making a massive superhero blockbuster film is a complicated process with all the digital effects and green screen that tends to be involved, but it turns out sometimes just reading the script can be equally difficult. Recently, Paul Bettany and Elizabeth Olsen appeared together for a Q&A at a regional comic-con, and the pair admitted that they both got really confused the first time they read a Marvel script. In the case of the man behind Vision, the confusion came from not actually being all that familiar with the characters beforehand. According to Bettany...
In England, in the seventies, comic books didn't seem to be such a big thing for us and so, when I was first doing these films and I was reading them, I was like, 'When's Iron Man going to come in? Where's Captain America?' They've got like 'Tony' and this guy called 'Steve' -- who are these people? It was the most confusing [script].
It probably seems almost funny now, as even people who didn't grow up with comic book characters like Iron Man or Captain America all now know who Tony Stark and Steve Rogers are, but there was certainly a time where that wasn't the case. While Paul Bettany had actually been part of the Marvel Cinematic Universe since the beginning, as the voice of Jarvis, he only became a tangible character in Avengers: Age of Ultron and may have only really begun to pay attention to the larger MCU at that point. As somebody who wasn't super into comic books as a kid, he knew the names of the heroes, but not necessarily the names of the people who wore the costumes.
However, that's not the only reason that Marvel scripts can be confusing as hell. Elizabeth Olsen reveals during ACE Comic-Con that there is apparently no consistency in these scripts when it comes to naming people at all. Even within the same script characters will be referred to by different names, which can also confuse you if you're not sure who everybody is.
Sometimes they just use last names, and sometimes they use first names, but it changes throughout the script... The first time reading one of these scripts was really [hard], like trying to draw pictures and diagrams and try to figure out who's who.
Elizabeth Olsen joined the MCU in Avengers: Age of Ultron so there were certainly a lot of characters that she needed to keep track of and if the script kept changing the way it referenced them it makes sense that things could get confusing. You'd need to keep notes with you so you remember which name(s) go with which hero.
Of course, this issue is only compounded when the number of characters increases, meaning the scripts for Avengers: Infinity War and Avengers 4 were probably near indecipherable. By now, of course, they're probably experts on all the names of Marvel characters. Just in time for everything to change when the current phase of the MCU comes to a close next year.