It's your worst nightmare. You're hauling down the trail, coming in hot to an unfamiliar corner. Round the apex and in your way is a jumbled mess of rocks, glass, and what may very likely be fresh horse droppings. There is no way you want to run into that stuff. You grab a handful of brake lever but nothing happens. Soft, squishy, and underpowered, there's no missing it now. You plow into the mess of debris and down you go. Replace those worn out pads with genuine Shimano J04C Metallic Disc Brake Pads and next time, have the control you need to steer clear of what may lie around the bend.