Historically whenever it comes to something I don't understand, I tend to make massive assumptions about whatever it is, mainly due from a place of ignorance and not have experience in a lot of things "non-technical". If it's something to do with technology, more often than not my intuitions are spot on. However if it's not entirely related to technology this is not usually the case, and there is no other area that I made as big of an incorrect assumption as I did as to when it came to running a business.
A few years ago I started a tech company and made a pretty big assumption that we would be able to seamlessly pull off our technology and business goals. While I was more or less correct about the technology goals, I was extremely off-base when it came to running a business, and foolishly I was under the belief that most of running a successful technology business, was just having good tech. I grossly under-estimated what I (now) think is the biggest factor in running a business, the people factor.
You can have as great technology skills, and tech products as humanly possible, but if your "people game" is poor, then you're basically fucked, and there's all sort of areas where different human dynamics come at play. It can be talking to clients, trying to raise money from VCs, or even dealing with your own employees. I won't pretend like I've figured this out, or try to prescribe some half-assed piece of advice, because truth be told, I think I still suck at the human dynamics of business. I'm definitely a lot better than I was when I first started the company, but I still have a long ways to go.
One of the interesting things I learned is that this human dynamics didnt come into play right away. In the beginning it was myself and my cofounders working closely together, and that was it. One of the cofounders I had known for a few years and the other I had a pretty good relationship with, so this lead to me believing that business was actually easy. I had started the company, was making stuff, we were progressing on our technology goals. That was it right? Nothing else mattered.... Nope.
It wasn't until we started trying to "sell ourselves" and get people using our products that I realised what an unbelievably incorrect assumption I had in that running a business was easy. Dealing with your own employees while it may occasionally be difficult is overall pretty easy. It's dealing with other people, other businesses that you really start to realise it's not that easy. Other business and people can be absolutely selfish and self-interested, which is somewhat understandable as business can be pretty selfish. But you will have people that try to steal your hard work, that routinely undermine the best efforts you're doing, and do everything they can to make sure they succeed, even if it means causing you to fail.
In the beginning when I first started running into these issues it was incredibly frustrating, and I spent so many hours brooding over mistakes I made, or people choosing over vendor services over ours. In the end however I learned that not worrying or obsessing about little things like that gives you a much healthier state of mind, and even makes you more likely to succeed. Learn from those opportunities and see what you can do better next time. Business A goes with Vendor C's services not yours? Ask them (politely) what made them pick the other vendors services. Sometimes it can be a simple thing like "oh we know other people using their services", but perhaps there was something about your offering they found undesirable. The only way you can improve those things is by finding out what they are. Sometimes it might hurt to hear someone say something bad about the work you do, but only hearing positive things won't help you improve the negatives.
The one thing that I personally haven't been able to "get over" is having other businesses steal your work. I won't name any names to keep things neutral, but about a year ago we did some work with another business, we sunk tens of hours into this, they were greasing the wheels making us feel good, enticing us to do some open-source work which is something we are very passionate about. We finish the work, set it up, demo it and then they vanished. They pulled the rug out from under us, took the work, and started selling it on their on. They ignored our emails, even tried to remove our original MIT license from the work, and it was crushing. And the shitty thing about this is that the amount of money it would've cost to sue them and take them to court would cost infinitely more than the money wasted during our hours of work.
That's about all for this rambling, peace!