A Few Random Thoughts
I think this is my third 'random thoughts' article and it's going to consist of some general thoughts about strength training. They aren't in any specific order or associated with one another but hopefully they provide some sort of use to your training.
1) Rate of force development isn't that important in powerlifting. Whether you reach your peak maximal force after 0.15sec or 0.30 sec is pretty irrelevant due to the relatively lengthy time it takes to complete a squat, bench, or deadlift max. The only reasonable argument that I've heard of would be that higher force earlier in the contraction might allow slightly greater momentum in the middle which may help ride through a sticking point. This effect I think would be pretty small though and irrelevant to most powerlifters who don't have a sticking point in this area of the lift.
2) If someone can't hit depth on squats and you're using good technique otherwise it's usually an ankle mobility issue so start with that if you're troubleshooting the problem.
3) There are a few different ways to overcome mental blocks on certain weights. This is fairly common and generally occurs at a certain milestone of 20kg plates on the bar such as a 140kg bench (3 plates each side) or with a weight that you've previously failed on one or more times. To sort this out you could try getting super amped up to over ride any fear/doubt which can work well for some people, generally those who are more experienced and can hold their form at high levels of arousal. You could use a reverse band set up where the weight at lockout is at or above the target weight to get used to seeing it on the bar and feeling it in your hands.
Without bands you could overload at 10-20% over the target weight and hold the weight at lockout for 5-10sec and then rack it if the set up is viable (eg on squats and bench). Another method that can work really well is to sneak the weight onto the bar so the lifter goes into the lift thinking it's a little lighter than it really is. The key here is that the lifter must be going into the set ready for a heavy load and you should be very confident that they'll have the strength to complete the lift. Sometimes just loading smaller weights can help if you're training alone so instead of three 20kg plates each side you might have two 20kg plates and a 10kg, 5kg, and a couple of 2.5kg plates.
4) Building muscle is a key aspect of strength training, as such it's probably a good idea to understand how to build more muscle. In this vain I think the absolute key driver of hypertrophy is mechanical tension with a little help from metabolic stress. I don't think the metabolic stress is as important as some people make out though - for example sets of 10 reps and sets of 20 reps to failure are known to promote similar levels of hypertrophy. If metabolic stress played a huge role then I'd expect to see greater muscle gains when training at 20 reps due to the additional metabolic stress, but we don't see that. I think the primary mechanism here is that metabolite accumulation increases motor unit recruitment placing more mechanical tension on the more responsive (to muscle hypertrophy) type 2 fibers which creates the growth response. A takeaway as far as muscle gains go is that if you're a strength athlete with sore elbows and you want to get some extra triceps work in then going higher reps on triceps extensions for example with lighter loads will likely be just as effective as heavier loading, and your elbows will probably feel better for it.
5) Focus on your own progress for the most part. Taking a look at the strength level and progress of those around you and on social media can be motivating and push you to train harder but at the same time try not to let it get you down if you don't feel like you're keeping pace. If you're on a solid training program, executing the sessions with good intent, working hard, nailing your nutrition, and getting plenty of sleep there isn't a whole lot else that you can do. If you and a friend are working equally hard in all aspects but they're making a ton faster progress than you are they've probably got their parents to thank (genetics, I'm not dissing your parents parenting skills). I definitely aren't encouraging people to make excuses about their genetics or limit themselves because I think everyone has the ability to get pretty damn strong and reach a good level of competition should they wish. But if you've been deadlifting consistently for five years and pull 200kg then it's unlikely you'll ever pull 400kg (presuming your program and recovery isn't an absolute shambles). I'm always a bit tentative at mentioning this because plenty of people do write themselves off way too early but I also see people ruining relationships and being generally miserable chasing a level of performance outside what is realistic. To clarify - I believe everyone can build a great deal of strength but I don't believe that everyone can be a legit world champion strength athlete no matter how hard they work.