For nearly as long as I’ve been aware of video game genres, I’ve been aware of the term “immersive sim.” Although it wasn’t the first game I played under the banner, BioShock was the first game I was aware of being an immersive sim. Sure, the concept of a game that emphasizes player choice worked in my brain, but it seemed like an unnecessary label. This was an era where a ton of open-world games were coming out, and it seemed like player choice was kind of the norm. That was nearly 15 years ago, and just this week, I’ve finally come to understand what precisely an immersive sim is.

I recently bought the first three Thief games. Developed by Looking Glass Studios, the same developers responsible for essentially creating the immersive sim with the Ultima Underworld games in the early-1900s, Thief came out in 1998. The game places you in the shoes of Garrett, a master thief in a Victorian Era-inspired metropolis called The City. The first mission in the game finds Garrett tasked with stealing a scepter from Lord Bafford’s manor.

The task seems simple enough, but I spent nearly all of my time playing so far in that single mission, totaling just about two hours. From the moment I was dropped down on the cobblestone sidewalk outside the manor, it clicked! I understood what this elusive feeling of an immersive sim was! While I wasn’t literally in Garrett’s shoes, I may as well have been. I slowly made my way around the side of the manor, sticking to the shadows and peeking around corners so I wouldn’t be spotted.

While I failed multiple times, which can only be read as “died,” I finally beat the mission. Making my way through the manor itself drove home that feeling even more. I learned guards’ walking patterns, the sounds that different materials make when they’re walked on, and made great use of Garrett’s water arrows to put out torches along the way. It only took half my life, but I finally understand what it is that makes a game an immersive sim. In light of that discovery, it makes me more excited to go back and play something like BioShock where I can truly understand what they were going for.

As I watched the mission complete screen come onto my monitor, the immersive sim concept clicked. This was a game that really let me figure out my own way to accomplish the objectives it gave me. Everything I was doing was intentional, and it was certainly possible that someone did this their own way. While I had my doubts with immersive sims being their own genre, they were thrown by the wayside when I saw the world through Garrett’s eyes.

Thief is available now on PC via Steam.