It seems to me that a lot of people run into problems with their horses because they forget one simple piece of knowledge, and that is that HORSES ARE ALWAYS TALKING TO YOU. Once you grasp that fact and understand that, whether you are aware of it or not, you are constantly having a conversation with your horse, I think a lot of problems can be avoided and a lot more success can be had.
It's the same as any interaction with another human, or a dog or cat or any living thing with a brain. You want to work and interact with it, you have to speak with it. Imagine working with another human. The two of you will talk and use body language to get along and complete the task. You wouldn't get very far staying silent and being ignorant towards each other, yet somehow you can see this a lot as people try to work with horses. The horse will be practically SCREAMING at the human, and the human continues on completely unaware of what's being shouted at them. A lot of times you'll see the horse get blamed for 'bad' things it's doing - when all along the horse has been yelling at the top of its lungs that something is wrong. I'm not saying horses can't just be disobedient or 'bad'; there are some rare, genuinely BAD horses, but honestly A) the source of the problem is almost always a human-caused issue or B) the disobedience could have been avoided if the humans just shut up for a second and LISTENED. Can you imagine voicing your opinion, again and again, a little louder each time, and continuously being ignored? How long could you go without getting fed up with it?
Horses can't speak, obviously, but they are still ALWAYS talking to you through body language - they're not shy about telling you what's going on, how they feel, and what they're thinking. And, whether you realize it or not, they're always listening to your feedback. So what are you telling them? Is it something understandable? Is it something relevant? The sooner you open your eyes and understand that there is in fact a conversation going on, the sooner you can wake up and become aware of what you're contributing to it.
Of course we are two entirely different species - not everyone is going to pick up the horse's language just like that. And the same goes the other way - young or unhandled horses are going to take a little more time and care to learn to understand us. It takes a lot of time and experience to be able to 'read' horses - it's a learning process that takes years. But some things we 'say' can be understood by every species. Fear, confidence, kindness, fairness etc are things, different types of energy, that everyone can understand...though it would seem that this is an aspect of our nature that a lot of humans have fallen out of touch with. A product of the internet age, I guess. There's a reason there's a saying 'It's not WHAT you say, it's HOW you say it.' Do everything with confidence and be sure of everything you do and you're already halfway to success.
So the next time something is going wrong or not working with your horse, just take a deep breath, a step back, and consider for a moment exactly what it is you're telling this horse - and what it is telling you. Regardless of your age or experience level, you're going to be a good step ahead if you have the ability to listen and the desire to make an effort to communicate and be understood.