Every single person I've ever met has a dark side. You find it eventually. Watch out for the people that hide their dark side as long as possible. Or even worse, pretend they don't have one.
No one is perfect. Everyone has anger, fear, sadness, shame, and a host of other negative qualities.
Let's step back and define nice. A nice person is one who tries to get you to like them. They want to be friendly and amciable.
They tend to hide their truer motivations and preferences.
In business, this is a big red flag.
I meet friendly people all of the time who want to be my friend and after they feel I like them enough, they try to sell me some shitty sales tool.
Now, I'm not saying don't be polite and respectful.
Nice != Polite and Respectful
Nice is trying to get someone to connect with you on a personal level. To use your emotional brain to overwhhelm your rational mind.
Why is nice so dangerous?
Nice is a safe default. Newcomers to certain businesses will be nice by default because they simply don't know what they're doing and they don't want to piss anyone off. Many good people are likeable and nice too.
But secret assholes pretend to be nice too. They want to evoke a jovial reaction so you're not thinking about the numbers and what's actually good for your customers and employees.
Stop valuing nice. Value respect and decency. Decent people aren't always nice but analyze their actions. Do they create fair deals? Do existing business partners want to continue their relationships into the future? Do they respect your time and try to add value to your business?
The motivation in business is usually money. That's the safest thing to assume. Anyone pretending otherwise is a wolf in sheep's clothing.
I trust people who are willing to show their dark side and illuminate their motivations. I trust people who have little time preference and value respect over compliments.
Don't trust people simply because they use friendly words.
Nice correlates with nothing useful for improving your business.