Who you hire matters.
While "a great employee can improve a company … a sour employee can hurt the culture of a company," says Liz Wessel, the co-founder and CEO of WayUp, a site that connects students and recent grads with jobs at places like Uber, Goldman Sachs, and Google, where Wessel previously worked.
When vetting prospective employees, the start-up CEO wants to know how creative they are and if they can be flexible in any situation.
"The two qualities I tend to look for most are if the person can be flexible and can think out of the box," the former Google employee tells CNBC.
"Flexibility is so crucial when you're working in a fast-paced environment like a start-up because things change really quickly. The people who succeed will be the people who can shift gears when needed."
How does she pinpoint the flexible and creative individuals?
She asks an uncomfortable question.
"I like to see how they react and whether they're able to stay calm," Wessel explains. "I don't do this because it's fun — I do this because I want to see whether they can keep composure and how they perform when they're out of their comfort zone, which is often the reality in the start-up world."
The WayUp CEO also isn't afraid to take her time. "Hiring slowly can be painful when you know you need someone to start right away, but few things are worse than firing someone who you never should have hired in the first place," she says.