- You're too fat - That's right, you're too fat. When you have a big gut in the way of the pull, it makes it a lot harder to get down to the bar, and actually increases the ROM in the movement because you can't get long in the arms. The deadlift isn't a lift that's impacted by weight gain or loss as much as the bench or squat. So if you're a really fat guy or gal, and your deadlift sucks, drop the gut.
- You're trying to "pick the barbell up" - I know this sounds strange because all you ever read is "the deadlift is just picking shit up off the floor". But that particular "mental cue" often keeps guys from understanding the importance of getting their legs involved in driving the weight off the floor. If you watch someone pull and see that when they initiate the pull, their hips pop up and sort of stay in that one area throughout the pull until the very last second, it means they aren't allowing the legs to drive the weight off the floor, and are asking the low back and hamstrings to do ALL the work. Once you learn how to get leg drive involved, or can think about the legs "pushing" the weight off the floor, your deadlift will jump rapidly, and your speed off the floor will improve tremendously. This should also let you know that it's leg strength that helps with speed off the floor. And that deficit movements aren't the key to improving speed off the floor. It's leg drive that is lacking.
- You aren't getting long in the arms - I sort of covered this in the "fat guy" one above. Basically, you need to get long in the arms on the pull. And a lot of people get so "tight" that they also bend at the elbow and get a small amount of scapular retraction before they pull, i.e. pull the shoulder blades back. This is a big mistake. The arms should actually be relaxed, but the grip should be tight. Not only that, if you're bending at the elbow, then you're asking for a blown bicep eventually. Let the arms hang, but keep tension in the glutes, hamstrings, lats, and grip.
- Your toes are killing your lock out - Lots of guys think they have trouble at lockout due to a lack of upperback strength (that's a different topic). But many people have trouble at lockout because they can't get their hips through, or have lazy glutes. Think about it, the last few inches of the deadlift is just getting the hips through and finishing scapular retraction. The reason a lot of guys suffer with lockout is because their glutes are just sitting back there, and aren't engaged in the lift. And for many of those guys, they can't get the glutes involved because they don't have enough external rotation of the hip, i.e. their feet are facing forward instead of pointing slightly out. The glutes can't contract maximally without some external hip rotation, and that can't happen if your toes are facing straight ahead. If you're having trouble at lockout, try pointing your toes slightly out and think about "getting your hips through" and see if that doesn't help tremendously.
- You're training the deadlift too heavy - I spent years frustrated with my pull, and the common cycle with it would be something like this....It goes up quickly - It stalls - It regresses - Frustration sets in. One thing I've said about the deadlift for a while is that it generally takes more than it gives back. That means, for a lot of guys, training the pull heavy often takes a great toll on recovery, and fatigues the hips and erectors for an extended period that is difficult to recover from. When I was developing Base Building, I quit training the pull heavy, and took a cue from Andy Bolton and really started focusing on speed with weights in the 75 - 85% range, and stayed away from 90%+ for a long time. It wasn't that long after that that my deadlift resumed progress again when I did decide to test it. I would feel fresh, and strong in the pull. Now I'm at a point where I am stiff legged deadlifting my former rep PR's from a deficit. If you're built for pulling, you can get away with heavy deadlifting far more often than a guy not built for it. So if you're not built to pull, try getting away from pulling heavy all the time, and pull lots of triples in that 75 - 85% for a while emphasizing getting faster with those weights, and test after a few months. I think you'll be pleasantly surprised.
- You're not training the deadlift - I went through this for a long time as well. "If you want a big deadlift, don't deadlift." Maybe that works for a guy here and there, but for the majority of lifters, they will actually need to train the deadlift. And by train the deadlift, I don't mean rack pulls and shit, I mean the pull from the floor.
- Your hips are too low - If your hips are too low and you're trying to start the pull with your hips low, then you're actually not in position to have leverage over the bar. Someone may point to a guy like Misha or Capt. Kirk and point out their huge drop in the hips, but if you watch the bar doesn't start coming off the floor until the shoulders are over the bar, and the hips are higher. And that's the position you have to be in before you can get leverage over the bar. The shoulders OVER the bar, and the hips higher. I've read before that you need to get the shoulders behind the bar, but you literally cannot deadlift off the floor with the shoulders behind the bar. I have no idea how that idea got circulated but it's literally bio-mechanically incorrect in every way. Have someone video your pull from the side. If your shoulders are not over the bar, then it means your hips are too low to really be able to apply maximal force to initiate the lift. Get your hips higher, and get a higher pull.
- Your posterior chain is weak - To pull big you need strong glutes, hamstrings, erectors, rhomboids, and traps. So you need to do support work to strengthen any of those areas that may be holding you back. You don't have to go bananas in finding support work to do that, i.e. doing 15 movements to accomplish this. A stiff legged deadlift will hammer the hamstrings, glutes, and upperback tremendously. Throw in a solid row and for the most part, you're covered. If you're really a support movement whore, then add in chins or pulldowns to the mix. At that point, you're literally covering all the musculature involved in the deadlift on the backside of your body.
This may not cover every single issue as to why your deadlift isn't moving as well as you'd like, but it generally covers the most common things I see or have seen as to the reason why a dudes deadlift has been stuck.