Insight is one of the currencies in Bloodborne, but it's also a mechanic that affects the gameplay.
There are MASSIVE SPOILERS below, so turn back now or one of Bloodborne's gameplay mechanics will be SPOILED for you.
Just like Blood Echoes in Bloodborne, Insight is used to purchase certain items from vendors in the game. But the amount of Insight you have on you will also alter the game's difficulty. Enemies will use more abilities in their attacks and sometimes, new "things" will appear.
YouTube user Michael DeLaGarza captured a video that shows an unspeakable horror appearing in the game world once you have 40 Insight.
What's Insight? Where can you spend it? Answers to these questions and more can be found in our full Bloodborne guide.