Why do we find it difficult to stay motivated?

The other day I wrote all the things motivated people wouldn't do, and that brings me to this thread.
1. Fear of failure and rejection.
Usually, when I sit down to write I have that fear of what if what I write isn't good enough? And that kind of fear holds me back. We all have these kinds of alarm reactions in our head that prevents us from moving forward. They are often related to failures or rejections in the past, that makes us afraid of walking out of our comfort zone.
2. Procrastination and avoidance.
We procrastinate and tend to avoid things that could make us uncomfortable or anxious. It is a kind of defence mechanism that we involve ourselves in without common knowledge. Sometimes, procrastination points us towards the right choices. We often see ourselves procrastinating over something we don't like.
3. Self-fulfilling prophesies and self-expectations.
I often find myself setting really big goals to be achieved within a short time span. While it might seem like it increases our motivation and arousal to do something, it's dangerous. It throws us into an endless spiral of worries and disappointments. And I think as human beings, we also try to fulfil societies label of who we are, and that drives a hard bargain on our personality and well-being.
4. Negative self-esteem.
No matter how much we motivate others when it comes to matters of our own self-esteem we are always doubtful. It affects our motivation to perform and love what we perform.
These are a few reasons I found that keep us from being motivated and achieving our goal. Feel free to add more in the comments down below.
Spring ;)

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@colourfulSpring22
I find that the fourth point is normally the main reason why I'm not always motivated but I'm working on it! I also love the quote you shared with us, a very good perspective. Wishing you the best, Lauren xx
*huggles* 
@blossombreathe, we all are always working on it, aren't we? Good luck, Lauren.
@colourfulSpring22
What if I lose the motivation when I'm already into something? I've lost my job 3 times already. I didn't last more than 8 months at either job and they were all in my niche: programming. It's my passion. But I still lose motivation. For example: "I'll be late today. I know it will lower my reputation, but I just can't get myself to stand up, look in the mirror and tell myself that I can do this." and I have no reason for being late other than, I have depression.
No employer has ever taken that seriously. I told an employer once that I have depression and that's why I'm not always cheerful, so I got fired a week later with the reason "we just need to downsize a little".
If business and depression don't mix, how can I do business while suffering from depression?
@fearlessHuman7431, I am sorry you feel this way. But always know that you are capable. Depression isn't something you should be ashamed of. Try to consult a therapist, they could teach you to strike a balance between things that can trouble you in life. And always remember, you are your own boss. You can do this. Sure, it will take a lot of time. A whole lot, but make little progress everyday. It will add up in the end.
@colourfulSpring22 thank you