Why is it so difficult to stay sober for some? Do they perceive much more pain? Is it sense of failure? Or is it something else?

Let's stop with all this "emotional pain" stuff. Everyone has emotional pain. Only a fraction of us become addicts.

Alcoholism (and addiction in general) has been shown to be as much as 55% genetic, meaning we often see families with generational addiction. For these addicts, the body actually metabolizes alcohol in a different way than does the normal system. They tend also to have neurochemical imbalances and irregularities in similar parts of the brain. These parts of the brain deal with recklessness, impulse control and novelty seeking.

This last part can also effect those with deep trauma or environmental pressures who choose substances to cope. Because after drinking (and drugging) begin, the brain begins to change, as does every system in the human body. But the crucial area here is the part of the brain responsible for executive function. The more and longer a person drinks or drugs, the more this area is damaged, and it eventually becomes difficult to impossible to make decisions reflective of critical thought and good planning. After a while, the addict can't stop.

Many of us are deeply emotionally scarred and there's a theory afoot positing that we're born with a chemical deficiency we try to replace with nearly anything we can. But anyone can get sober. Keep in mind, abstinence is not sobriety. In order to give up all drugs, a full life shift has to occur and a healthy lifestyle adopted. This takes therapy and fellowship, not merely "emotional healing" or more willpower.

Lastly, relapses occur in stages. Emotional, mental and physical. By the time a person picks up, he or she's been in relapse for some time. This is why full and thorough sobriety is so crucial. People have bad days, sudden events, old triggers and frightening situations. We need to protect against those by prevention. The addict's brain doesn't function like yours; have empathy for that. There's a substance that will always call his or her name, like a siren. Learning to ignore it takes some trial and error.

I’ve struggled with addiction for about 5 years now, but I have struggled with mental illness for far longer than that, have had to live with ptsd and ocd for as long as I can remember.

I never received any professional help, so I spent most of my time searching for something that would shut everything out, even for just a little while. By the time I got help and wanted to stop, it felt as if it was too late.

Please understand that there is a spiritual emptiness in an addict's soul.
Barely material things or treatment of mental part is not enough.
Most people miss that part - those who somehow find some spiritual engagement in their lives are fortunate - others have to bring it in their lives.
Thank you

It’s an escape pure and simple, some people struggle to cope and instead of letting the emotions just be what they are, they mask it with various things. It’s not just substance abuse, it can be anything that allows you to escape your emotions

What brings them joy, the feeling of escape, also at some point couples with their pain and then becomes the pain itself, which then feeds the cycle of addiction looking for joy? I think it's something like that.

some are more prone to addictive behavior

A lot of times it’s mental illness

Define sober.

Same ffs

It is easy to forget that persons with addictions first begin using certain substances to deal with the pain of existence. As such, it is necessary to replace the controlled substance as a coping mechanism.

I've had as much experience with addiction as anyone could want, and my honest answer is that I have no idea.