Many of my clients have expressed a doubt in their decision-making abilities. When we've traced the origin of this belief, it often comes from different sources but it's also pretty frequently learned in youth (while the brain is still developing).
A person's self-doubt could stem from multiple things, among them:
a parent who was overly critical and never pleased, leaving the child to believe they could never do anything right or "good enough;"
a person's own failure in the past which lead them to believe they were defective;
growing up in a dysfunctional family where a person's decisions and preferences were never honored or respected;
social influences which have taught them to compare themselves to unrealistic standards;
or anything in this line of thinking where the person was lead to feel "not good enough."
Then this person grows up with this idea, or may even develop it in adulthood, having sprouted in their head that they don't measure up to arbitrary and ridiculous standards as a core idea of their efficacy as a person. This can lead to anxiety when they are tasked with something that they then believe they're unable to do. Or perhaps they don't know how to think or feel about it. And they may even hold unachievable standards for themselves, which they then can't fulfill and it becomes evidence to themselves that they're deficient.
Ultimately, the anxiety that comes can also lead to avoidance, which is a key trait of anxiety. With this avoidance, the person struggles to handle the task at hand because this idea of their own deficiency keeps them from wanting to tackle it. Their nervous system may also feel overwhelmed, leading to a state of feeling shut-down and unresponsive.
This avoidance/shutdown can reinforce the idea to that person that they are unable to trust themselves, when in fact their reaction is a normal way of the brain trying to preserve our well-being. It may not be a helpful form of preservation, but there's a reason it exists: Anything from avoiding discomfort to "playing dead" for an apex predator (an older evolutionary trait still embedded in the "lizard" part of our brains). The bottom line is that your reactions are normal. They may not be what they need to be, but you can continue to work towards changing that.
Ultimately, the lesson is to learn how to take care of yourself, set reasonable goals, and give yourself a break while you still try your best. Understand why you don't trust yourself and work around that, because just calling yourself lazy and then trying to force yourself to do things is like self-flagellation: You'll just hurt yourself for no reason and then you won't be at your best to do the things that you want to do.