People don't underperform because they lack technical skills. People underperform because they lack soft skills.
"A few years ago, a senior engineering executive at a high-tech Silicon Valley company asked me to teach a two-hour course on assessing "soft skills". His company had mastered the art of judging candidates' technical skills. It conducted day-long interviews focused on programming languages, server skills, and data analysis. Then, in the final 45 minutes, the hiring manager would turn his attention to the soft skills. If felt like an afterthought, perhaps because it was.
...His immediate response was a stunned silence; the expanse and impact of a candidate's soft skills had perhaps not occurred to him before. I think he realized quite quickly that 45 minutes tacked on the end of an all-day interview was not enough."