This kind of reminds me of something Big Dave Tate wrote in his latest interview. The idea that powerlifters would be fried after a couple reps and bodybuilders wouldn't be able to squeeze everything into a few reps. To me, metabolic subtlety aside, that speaks to focus.
You have to learn how to produce force. It is a skill. Training in the weight room should be as much practice of skill as it is pure conditioning value. Here's some bullet points I've gleened form various sources as well as fabricated for myself as regards focus:
-Visualization. Lots of good stuff out there about this. Mike Robertson has an article and Brooks Kubik wrote alot about it in Dinosaur Training. I like to visualize that I'm walking down a path jam packed with barbarian warriors, with only the narrowest space in between. (I'm a pacer, by the way, so this works nicely with how I pace around the gym in between sets.) They're screaming, usually the word "UP" or "KILL" and it's deafening and the sound rattles my skull. Everyone in my gym is something these barbarians are ripping limb from limb or burning or attacking with clubs and swords. The equpiment is bears, other beasts, stone monoliths, anything else to set the mood. The drinking fountain is a murky pool and the walls are granite cliffs. When I get to the platform or the power rack, it too is set in the middle of this barbarian horde, and they truly work themselves into a frenzy when I address the bar. Then you let 'er rip. Visualize yourself performing too, how your body is positioned the way you want it to be, how your performing exactly how you'll want to for real. Yet another visualization tool is flashing the color red. Red as in blood, fire and war. There was a study Kubik wrote about that the color red in the form of a flashing light caused the greatest forces on a grip dynamometer, whereas other colors had no effect or lessened force. Visualize the color red flashing before your eyes, even painting what you see in red overtones. Visualizing blood, fire and war works for me too.
-Vocalization. I like to make up a "diddy" to say before you execute. Now, these can be used as a learning tool, like when Dan John says "Check" when someone is doing an )-lift (Read DJ's Get Up!, you'll get it.", but I use these as a psych up tool. I'll say "bend the bar" or "crush" or "up" whatever. The key is to just boldy say it out loud, with no concern over who might hear you or what you look like.
-Positive self talk. I think in Dr. Singer(?)'s interview he says how you should only use positive self talk. Never say "I can't fail." say "I will succeed." Don't say "I can't miss this" say "I will lock it out." It's easy. I've done it before. I can get this, so on an so forth.
-Sometimes a good slap in the face does wonders to bring me back "in the moment".
Hope some of that helps you. Now, please bear in mind, I don't use all of that all the time. That's for when I want the MAXIMUM amount of psychological arousal. There's supposed to be an optimal amount of psych-up, too much is as bad as too little, you have to find the sweet spot. Also, don't use these for evrry exercise all the time. No need to go through this whole routine just for face pulls or terminal knee extensions. I actually have to tone down my psych up on my lighter days to keep from getting burned out.