I would like to contribute two things from observation: I think what is difficult for many is the complexity of a project, which is sometimes insufficiently explored. And also in the requirements away from the core business, problems can easily arise. A carpenter can create great furniture, but may be uneducated when it comes to tax aspects or marketing. Not only does this mean he can't do it himself, but he also has a hard time assessing third party qualifications or price/performance. How often have people been sold a junk website, absolutely not up to date or fit for the future, and the clients took it off? As a result of a junk website would be losses in SEO us therefore less clicks & sales, annoyed prospects, vulnerability and much more.
Especially fiscal aspects can quickly shatter dreams with insufficient advice/knowledge. One makes oneself here and there faster punishable than one believes (at least in the country in which I live).
Just my subjective opinion...
What helps? Planing, planing, planing and building up a good team/relations/networking.