Here's an example from a recent client of mine. She is a naturally nice and caring person and she always identifies herself with the team she is part of. She likes to bake, so she used to bring cookies and cakes to work. She is empathetic, so she used to listen to her colleagues stories, sometimes at the expense of her personal time after work, and encourage and support them. She collected money and bought gifts for their birthdays, and she thought that she is surrounded by warm loving people who care about her as much as she cares about them. And then an accident happened in her family which caused her to miss two weeks at work. Her boss who she supported so actively refused to give her any flexibility with work time or to allow her to work from home. Her teammates who she considered almost family refused to take over her projects temporarily to help out in an emergency. Her world was falling apart and even more so when she decided to leave, and her colleague told her the team was relieved to see her go. He said, "We loved the food that you bring and that you always listen to our problems, but you work hard and establish such a high bar that the rest of us look bad."
We may sympathize with my client above, but we should not. While she cared about her team on the surface, she failed to establish trusted relationships with them. When you join a world-class company such as a Big 4 consulting giant, your day 1 of training starts with this one: importance of building relationships. It does not start with sales tactics or consulting techniques - relationship building is prioritized above everything else.
So what does it mean to build relationships? Does it mean to learn person's name, the names of their kids, hobbies, and stop by this person every week to say "hi" and to ask how family is doing or invite to lunch once in a while? Well, maybe yes, but this is not what is meant by relationship building in a professional environment. The importance is placed on creating trusted lasting relationships, whether it is your client, colleague, or boss. Openly exchanging information, supporting when things gets rough, taking over a task or two without announcing it to the world, giving advice, providing a template, fixing compilation error - doing whatever it takes to genuinely help this person succeed.
In my recent experience, there was the following example: an internal recruiter was working with a hiring manager to fill a new position. They collaborated well until the recruiter mentioned in a weekly update to his boss that this hiring manager's calendar is almost completely booked and he is concerned that some of candidates won't wait until she is available. Recruiter's manager escalated this problem to the manager of the hiring manager informing him that this person's availability puts the whole hiring process in jeopardy. Eventually, the relationship was broken resulting in inability to collaborate in the hiring process. Meanwhile all the recruiter had to do was to tell about his concern directly to the hiring manager who was unaware of his challenge.
This does not mean that you should always be unnecessarily nice or not raise concerns or not provide feedback. Raising your concerns directly to the person in a positive way is a sign of respect. Raising concerns to this person's supervisor (even indirectly, such as in a weekly report) before talking to this person damages trust and is not helping in building healthy relationships. If you feel that someone is not fully honest (e.g. withholding important information or not sharing meeting details), call this person out, but do it as a question in a respectful but committed way and in private.
Build relationships via collaboration, through inspiring others, by thanking them when they support you. Do not assume that relationship building will come by itself, it requires gentle nurturing and care.