The ability to keep promises is one of the most important qualities many people look for in friends and partners.

Donna Morris, Walmart’s Chief Human Resources Officer, also looks for this quality in her employees. The 57-year-old oversees 2.1 million employees and serves as the company’s vice president. She says that for her, the most obvious quality in an employee is the ability to deliver on their promises.

According to a CNBC “Make It” report focusing on entrepreneurial leadership, Morris said, “They deliver the results you expect, when you expect them.” She believes that the best employees often complete tasks ahead of schedule, “so I would say it’s always better to finish early than late, and it’s always better to finish more than less.”

She points out that integrity and trustworthiness are among the qualities she looks for most in her hires, as managers want employees who not only get the job done but also are willing to go the extra mile in the workplace. Leadership expert and author Scott Mautz, in another article for CNBC’s “Make It,” notes that these qualities can also help you rise in status and gain respect among your colleagues.

Besides reliability, Morris admires employees who are willing to take on new challenges. “They raise their hands, take on more, and don’t push back,” she says. “People who are willing to say, ‘I’ll give it a try,’ even when they have a lot on their plate, definitely possess this quality.”

It’s important to note that taking on more than you can handle can backfire. LinkedIn career expert Drew McCaskill warns that this can severely damage your mental health and productivity, so you should only take on work you truly have time for.

“Don’t expect to earn extra credit for working harder,” he says. “When work is causing you sleeplessness, anxiety…or making you feel overwhelmed, speak up.”