Can a lack of diversity cost a company its key talent? That’s a question confronting many tech firms as they make very public attempts to diversify their staff. Among those companies is Twitter, which recently issued its diversity data for 2015. According to an August blog posting on the matter, Twitter has a multi-pronged strategy for increasing diversity in coming years, including recruiting at colleges with underrepresented talent, adjusting its internal recruiting efforts, and partnering with organizations devoted to increasing diversity. But for one Twitter engineer, those efforts haven’t been enough. “Leadership keeps citing the pipeline” of tech talent as a reason for the lack of diversity “when the data does not support it,” Leslie Miley, a manager and engineer at Twitter, wrote in a much-circulated Medium posting about his recent decision to leave the company. “They continue to churn out ethnic and racial minorities and women but still claim a commitment to diversity.” Twitter’s reliance on certain schools and workplaces for sourcing talent, he added, made it possible for “a type of group think to dominate,” with “very little diversity in thought and almost no diversity in action.” All that being said, Miley expressed hope that once-and-future Twitter CEO Jack Dorsey will figure out a way to further diversify the company’s internal makeup. Despite much public handwringing over the diversity numbers at tech companies, data suggests that tech’s leadership remains overwhelmingly white and male, although the demographics shift a bit once you include all employees. It seems that tech firms have good reason to be concerned over the percentages; as Miley demonstrated, employee perceptions of a lack of diversity can lead to key employees leaving the company, which in turn can cause strategic issues.