Burn out – it's real.
Most car guys I've met don't like to admit it as a matter of pride, but it happens. In fact, it happens regularly – even if it isn't recognized.
It's actually quite common to find someone making great headway on a project, and then, all of a sudden. Bam. No more progress.
Sure, there are plenty of circumstances where momentum gets squashed by missing parts or life demands, but there are also plenty of times when a car crafter finds burn out rearing it's ugly head. In fact, I'd almost be willing to wager that it is one of the most common de-railers of projects.
I understand that pride is a strong influence for not wanting to accept something that can seem like a personal short coming. The truth is, every person, no matter how tough they are or wish they were, will find their breaking point.
Every single person, whether you are an infant in diapers, a Navy SEAL, or the demigod Hercules – doesn't matter – you can only handle so much.
The important part isn't that you found yours, it's that you recognize and accept it, and perform the self care necessary so that a 1 week or 1 month break doesn't turn into a 1-10 year hiatus or worse – it becomes permanent.
Seriously, every person needs a break, and we each have different limits and ways that will best help us recover from running out of steam. The best thing you can do when you reach that point is to take that needed break, but do it in a considered way that will allow you to recuperate and get back on that horse – or under the car, as the case may be.
I would even go so far as to say, it's critical to have breaks planned into your project, because you are going to need them. Of course it slows down your completion date in a theoretical way, but in a practical way, the truth is, it speeds it up, because breaking and not rejuvenating yourself is a recipe for disaster.
Never is a lot longer than a break – even if it lasts an entire month.