Yep. I'm guilty. I tell myself at the gym that I need to go heavy, when that's actually NOT TRUE AT ALL! Yeah, there's a time and place for going heavy, but the Lat Pull-Down exercise is one that you shouldn't go too heavy on. Because of the movement and the angle of the back, it's vital to have absolute control of the weight, which means the weight needs to be challenging enough to bust out four sets of 12 reps.
I found this INCREDIBLE tip on how to trick out your lat exercise by another dude that I follow on YouTube. His name is Rashawn Winfree of Winfree Fitness.