People struggle to make progress not always because of physical factors but sometimes because of their own mind. People can often hold themselves back due to their own mental barriers they create, barriers which don't actually exist. I have written previously about how people often read too much and suffer paralysis by analysis in my post Do you know the difference between knowledge and wisdom?
There are a few areas which I think lifters read too much into and think matter more than they actually do.
First of all we have genetics. Now this is as very broad term which doesn't say much about why people hold themselves back because they don't believe their genetics's are good enough. So let's break down genetics into individual factors people think are more important than they are.
Limb lever lengths. This one comes up a lot. People think that unless you are built perfectly for a lift you will never be strong at it. You must have long arms, short arms, short torso, short legs, long torso, big rib cage, 7.567480943 inch wrists for you to be a good deadlifter, squatter or bencher. There is one thing which matters far more than any of these things. That is the strength of your muscles. Weight moves by the force your muscles apply to it. It doesn't matter how you are built if your muscles are weak you will not lift a lot of weight. What is far more important is to just focus on becoming as strong as possible. What's more comforting is when I attend powerlifting competitions I often see guys who look to be exceptions to the typical limb leverage rules. Long armed guys with big benches, skinny guys with massive squats etc. Now if leverages are based on physics and physics doesn't have exception it goes to show that there is more at play than simply how you are built for a lift. These guys exist because they are actually strong and don't hold themselves back thinking " I'll never have a good bench I've got long arms, its physics biggunz408 says so"
Body types. I'm sure everyone has heard of the three supposesed body types. The ectomorph, endomorph and mesomorph. Ectomorphs are the skinny hard gainers, endomorphs are the fat ones whose genetics area to blame for them being fat and mesomorphs are naturally muscular, lean and are amazing at everything. Some texts even go so far as to say a particular body type also has a particular personality and should only train in a certain way. Of course you're an ectomorph so you must be introverted and only lift in the 15-20 rep range. This is utterly ridiculous as if there are only 3 types of people in the world. No one really is an exact version of any of these and physical training and diet are what detetmines what your body will actually look like. So you are skinny, build muscle, you are fat lose weight, not paeticialy one or the other does that mean that every thing is given to you on a plate because you are a mesomorph? Just because you are not skinny or fat doesn't mean you find it easier to build muscle. It still comes down to training and diet. I wouldn't consider myself any of the 3. Before I started lifting I wasn't really fat or skinny or muscular I was just an average build. Now I'm more mesomorphic but wait, isn't that the point of training? To gain muscle and strength and lose fat? If you train hard and eat well you will achieve both of these things no matter from where you started. So if you are an ectomorph or endomorph you become a mesomorph through diet and lifting so in reality if those regimented body types do exist how is it then that you are able to change from one to another? Surely you can't change your genetics but you are able to change your body because lifestyle factors are bigger than genetic factors. So you think you gain fat easily because you are endomorphic. As you become leaner you make it easier to stay leaner. Insulin sensitivity improves, anabolic hormones increase, you build muscle which raises metabolism, you become fitter and your work capacity improves meaning you can work harder and do more. Your body is making its self more favourable to becoming muscular and lean. What if you are a skinny hardgainer. lifestyle changes brought on by diet and training suddenly make it easier to gain, increased appetite from an increase in bodyweight, more nourishing food which you may have been lacking before, increases in anabolic hormones such as testosterone from dietry fat and heavy training with compound movements, improved sleep from all the hard work, getting stronger which in turn allows you to train harder and heavier causing greater muscle gains. Once you start building muscle it can have a cascading effect making your body more favourable at making greater gains. Don't hold yourself back thinking you have certain body type which will hold you back from making progress. The only thing to hold you back is you.
Muscle fibre composition. There are 3 types of muscle fibres, type 1 slow twitch, type 2a fast twitch and type 2b super fast twitch. It is thought that those with superior genetics for explosive events have prodominenty fast and super fast twitch fibres while those who are superior at endutrence events have predominantly slow twitch fibres. Most peoples muscles are about a 50/50 combination of type 1 and 2 with a similar arrangement among the type 2a and 2b. Amongst these muscle fibre type 2a are the most responsive to change. They have the ability to adapt towards slow twitch (endurance) or fast twitch (power) depending on the demands placed upon them (training).
Equipment. It's possible to get strong using the most basic equipment. Yet lifters seem to think they must train at Westside and if only their gym had bands, chains, a reverse hyper, a glute ham raise, a prowler, sled, football bar, safety squat bar, chambered bar, or whatever then they would be able to make progress. Now the thing is guy's have been getting strong for decades before all this specialised crap by just using the basic lifts. Guys like Ed Coan and captain Kirk got to world class level with just regular barbell lifts and a few simple assistance exercises. Look at old time strongmen. They had even less equipment avaible to them and still achieved incredible strength and physiques. Even crappy commercial gyms have barbells and most have a squat rack. What more do you need? Even one guy called Milo steinborn wasn't going to let something such as the squat rack not being invented stop him from doing heavy squats and would simple up end the barbell get underneath it and perform squats. He even did it with up to 500lbs.
Supplements. Sometimes lifters feel like supplements make such a huge difference to them that they are unable to make progress without them. They are following the Anacoda protocol with indigo 3G and MAG 10 pulses throughout the day and would be useless without their morning 11 pills of animal pak. They must follow the best peri workout nutrition otherwise their entire workout is useless. In fact I don't think "peri" is even a word. The concept that you must consume very specific fast digesting nutrients around your workout is relatively new. Going back to many old school lifters and strongmen many achieved great things without any supplements what so ever. Now the thing is if you consume the same overall macronutritions in a day from food as you would from including the latest pre, intra and post workout nutrition do you really think its going to make a difference? The supplements may be faster acting so get to work sooner but they are still going to take hours to digest. When you finish a workout its the pre digested food that is going to kick start your recovery not your post work out shake. Don't think that a pre workout shake will make difference either as it will still be long after your workout when its nutrients are utilised. When you are doing intense exercise digestion is all but halted as your body moves blood away from the stomach and into the muscles. If you were to eat the same macros from food while it might not digest as fast it will be sustained over a longer period of time keeping your recovery ticking over for longer.
I don't mean to say that all supplements are a waste of money but I feel real food is superior. And don't hold yourself back thinking you can't make progress without them.
There may be other ways lifters hold themselves back mentally but I think this covers the main ones. Just remember there are no excuses and your force of will is far stronger than your body is. Break walls down