Context effect is the way your brain makes sense of what you see, hear, or experience based on the things that came before it or will come after it.
Imagine that you are reading a story about a person who is walking in a forest. If you imagine that there are big, spooky trees and animals lurking behind every corner, you will interpret the story differently than if you imagine that there are small, friendly animals and pretty flowers everywhere.
This is because your brain is using the context of the story to create a mental picture of what's happening. The same is true in other situations, like when you hear a sentence spoken by someone - the way you interpret what they say is influenced by the words that came before and after it.
Context effect helps us make sense of things that might otherwise be confusing or unclear. It also allows us to use our experiences and knowledge to interpret new situations in a meaningful way.