The more books you read, the more you tend to notice and observe patterns in the types of plots, characters, and settings that are written about. This can be especially difficult when it comes to mysteries and thrillers, where plot twists are often reused multiple times.
Once you’ve seen a plot twist used once, you essentially add it to a mental library of plot twists you’ve read before in other mysteries. Every time you read a new mystery, you try to compare all the plot twists you’ve read before to the mystery you’re currently reading, trying to figure out if one of those previous plot twists you’ve read can maybe be used to crack the case you’re currently reading about.
Mysteries are all about the shock; that “ah ha!” moment where everything is revealed. If you’re able to discern that plot twist before the “Ultimate Reveal” happens, it takes away a large component of what makes mysteries so enjoyable to read.