I'm not to the point where I use a mantra to get up hills, unless the mantra is "Remember what they said on TE, shift down, oh crap, I shifted up! SHIFT DOWN!"

But when I'm riding a flat and feeling tired and grumpy I tell myself that I'm not peddling with my legs, my feet are doing the work. It really does take my mind off my burning quads and owchie saddle problems I forget where I read this idea. Anyway, this translates into the mantra "feet, feet, feet, feet,feet". I also imagine I'm kicking out when I pedal, that seems to help me keep going and go faster.