There are some really great posts with excellent explanations for possible motivations and how they play out.
Sometimes people really have no choice in the situations they're in, or they have choices between several horrible things...the proverbial rock and a hard place. From my own personal experience, I have seen people stay in bad marriages because they're not financially solvent without their partner to make it alone, stay at thankless, unsatisfying, dead-end and low-paying jobs because they lack the education and experience to move elsewhere (which ties into the money factor because school costs money), stay in bad neighborhoods because they don't know a life outside of their zip code. Their self-esteem and confidence has been beat down so they don't even think they have the ability to do anything else or change anything in their situation.
Sometimes it's not about not being able to conceptualize and believe things could be better. I think many people are stagnant because they know and see their situation could improve but they lack the access, tools and knowledge of how to do it. It's like they know it's out there and they want it, but it's an ocean separating them from it and the thought of crossing that gulf is daunting and feels insurmountable. Sometimes it is...sometimes people do "die" along the way trying to attain something. Sometimes people traveling the path see the bones of those that have fallen before them or get so tired of fighting themselves they just turn back around. Some make it and some don't. That's just the fact of the matter.
For me, it's a basic life tenet that I be one of those that makes it, or dies along the way trying. Let my bones serve as a warning to turn back or a motivation to go forward (or vice versa). Life isn't easy and no one should be so tragically misinformed to think it is. There is a lot of figuring out if what I'm trying to attain is worth whatever the consequences of my efforts are. I think some stagnation also arises because people think (myself included), "Is it supposed to be this hard?" I believe that if you think the road of ahead you is something to be tossed in a microwave and fully cooked in five minutes, then you are bound to suffer disappointment, disillusionment, dissatisfaction and it's very easy for those feelings to competitively spiral downward into a muddy and dark pit. I'd much rather believe life is an obstacle course so that I'm training and ready to duck and dodge, than believe it's a cakewalk and encounter my first difficulty and crumble.
The belief that life is a breeze can work out well too. It's like that Staples, "That was easy," button. If you look at life's difficulties as things that are not insurmountable then you're more willing to climb over, dig around, under or through whatever problem is in front of you. If you believe, this is just a detour, this is not the end of the road then you may be able to give yourself the patience and forgiveness to begin to chip away at whatever the issue is.
I often use the scared straight method and fear to motivate myself: fear of losing my quality of life, fear of losing agency/control over my life, fear of being a victim of fate and circumstance, fear of being oppressed, fear of being taken advantage of.
Fears like the ones I listed above scare me more than fear of failure and jolt me out of inertia. I can always take solace in knowing I tried and I have taken solace in knowing I put up a fight, even if I didn't succeed. This isn't something that happens overnight. In one particular area of my life, it has taken me four years to finally be proactive, instead of hiding and hoping things would just would work themselves out.
When I do beneficial and healthy things for me, it makes me feel good and I want to do them again. They activate my pleasure centers. Bad things I do to myself also activate my pleasure centers, because oftentimes being bad feels good. What I try to do is play mind games with myself and associate bone-crushing negatives with the bad things that in the long run hurt me. I put a cause and effect into play...if I do this, then this will happen. Do I want that to happen? No. And if that happens this other thing will happen. So on and so forth.
I understand that the disconnect is between the will and the action, the trying and the doing. How do you get yourself over the hump?
A large part of me having the confidence to move forward in something is to educate and inform myself about whatever it is that's intimidating me so that it stops being this huge scary monster in my life. I look at it as turning on all the lights in a room so that everything is illuminated. The biggest thing I did is look for ways to educate and gain some control and agency and not feel like a leaf in the wind. Bite things off in small manageable chunks, don't set expectations for change too high in the initial stages. Spread it out over months if you can. Realize you will have false starts and learn how not to crucify yourself after a few false starts. If it helps, find someone else you have to answer and be accountable to.
When I first started seriously job-hunting nearly a year ago, I entered into a friendly competition with a friend of mine that we had to apply to four jobs per month. We had to forward the emails to each other as proof that we sent it. There was no penalty for not doing it, but I felt good for reaching my monthly goal, which made me want to improve my resume, which made me want to take my resume to networking events and job fairs, contact recruiters, and even send out cold resumes if I didn't see anything that I liked for that month but still wanted to reach my goal. Even though I haven't gotten a new job yet, I've had a couple of interviews and have gotten some excellent feedback on my resume. This makes me feel validated that I did do something that is indeed paying off.
I hate to say platitudes, but the feeling that you're accomplishing something snowballs and motivates you even further...even so much that you feel like you can take a few hits and not be floored.