A quick Google search reveals how many Internet articles tell you not to be nice at work, but in an article for Harvard Business Review, Emma Seppälä provides real evidence that it pays to be nice.
Seppälä draws varied information from several sources. For instance, healthcare expenses go up 46 percent in organizations with high levels of stress, proving that managers who think putting pressure on employees is a good thing are critically wrong. Stress also causes people to seek new jobs or decline promotions. On the flip side, as long as they do not become pushovers or enablers, nice managers fare much better. People who project warmth inspire trust faster and thus become more effective leaders. Even more interestingly, being fair to employees causes those people to be not just more courteous to the manager, but more considerate of and loyal to other employees in general. And since a 2013 Gallup poll shows that employees prefer happiness over high pay, this is a big deal. For even more facts on how great it is to be good, you can read the original article here: https://hbr.org/2014/11/the-hard-data-on-being-a-nice-boss