A time that I found myself “playing in the top left box” was when I caught a structure fire in what was thought to be a single family residence, but had actually been turned into a duplex. At the time, I was working for the City of Franklin Fire Department and was riding backstep on E-17. Upon arrival, there was a working structure fire with heavy smoke showing from the Charlie side. My first instinct was to pull the line to the front door as the officer did his 360. I didn’t even consider the possibility that the interior of the home had been modified and turned into a duplex, additionally not considering how this home may be broken up. After the officer’s 360 was complete and a brief conversation with the home-owner, we realized that this home was now a duplex and that the only access to the unit that was on fire was from the Charlie side. The line was then redeployed to the Charlie side and the fire was put out. The repositioning of the line took some time and I realized that there were several things I could have done to prevent the delay. The address had a half in its numerics, such as 105 ½ South Main Street. This should have made me consider the possibility of this residence being modified and think before I automatically pulled the hoseline to the Alpha side when smoke was showing from the Charlie. Other than being more aware of the numerics from the address, I learned that I could have slowed down and recognized additional signs that this residence had been modified, such as multiple A/C units, multiple electrical meters, address indicators and multiple mailboxes. This incident also taught me to slow down and not get sucked into doing the same thing on every fire (automatically pulling a line to the alpha side), because each fire is different and requires different tactics. Knowing your district is also a very important lesson learned in this instance. Had I been out more and studied my district, I may have known that several homes on this particular street had been modified into multi-family units. Overall, my biggest take away is to slow down in order to prevent the tunnel vision effect and know your surroundings, whether that is the scene that you are currently operating in or preplanning and knowing your district.