Relationships are one of the most important things in life, and I say this as a guy who could litteraly not talk to anyone for two weeks strait. It's relationships with people that get you your first customers for your start-up, your key employees. relationships keep you down to earth, friends and fmily. The latter being one of the most important elements in your life, your kids and spouse.
Why am I saying this? Because relationships go both ways. When you care about people, chances are some of them will care about you as well. And if you don't really care about your customers, your company is screwed anyway.
Granted, everyone has a different bandwidth to handle these relationships, and seperating the toxic ones from the rest is problem. Which makes relationships all the more important.
Being able to say "No", and being willing to let people down because there are things you need to do that are more important than them, is a really important skill when you're running a startup.
You can't succeed if you're giving up all your time to other people's things. You have to stop and tell them you won't do what they're asking because you're focusing on your own stuff. They will complain. Some of them will stop talking to you. You might really annoy your family. Your real friends will understand and still be there when you're finished. Some of them might happily come along and help you with what you're doing.