Warren Buffet once said "In looking for people to hire, look for three qualities: integrity, intelligence, and energy. And if they don't have the first one, the other two will kill you." Clearly integrity is the first requirement when hiring, but right behind it, is intelligence. Unfortunately, intelligence comes with its own baggage.
Intelligence is essential when hiring into a fast growing company. Intelligence enables quick problem solving and brilliant, innovative ideas. Intelligence allows people to work autonomously when they need to cut through to the solution at a faster pace while still arriving at a great result. Smarter employees take less time to train and less time to positively impact your business.
However, smart people can also have a hard time learning. Chris Argyris' 1991 article in the Harvard Business Review, "Teaching Smart People How to Learn" outlines the basic dilemma and ways to think about solving it (It's a must-read in my opinion). The dilemma is, the smartest people in the organization who are often assumed to be the best at learning, may actually not be very good at it.
"Put simply, because many professionals are almost always successful at what they do, they rarely experience failure. And because they have rarely failed, they have never learned how to learn from failure. So whenever their single-loop learning strategies go wrong, they become defensive, screen out criticism, and put the "blame" on anyone and everyone but themselves. In short, their ability to learn shuts down precisely at the moment they need it the most"
Brittle behavior, defensiveness and blaming kill a team's ability to solve complex problems together. When you are changing quickly and learning a market (which is a continuous process when growing fast) it is important that everyone on the team can learn from the facts that are emerging. When things don't turn out exactly as planned (which they never do), don't look for who/what to blame; just get on with finding the next solution.
The key to not blaming is to be introspective before blaming outside factors. What are my assumptions and beliefs that are holding me back from learning from this situation? Very smart people who do this naturally learn fast in complex business situations. Very smart people who are arrogant about their intellect typically don't. Struggling early (in school, in your first job); and/or experiencing failure is humbling. It forces you to look inside yourself, and with practice; develop the ability to check your internal assumptions before blaming someone else.
It's tricky, but you can figure out if a candidate is a learner in the interview. Chris Argyris' article points out: "One of the paradoxes of human behavior, however, is that the master program people actually use is rarely the one they think they use. Ask people in an interview or questionnaire to articulate the rules they use to govern their actions, and they will give you what I call their "espoused" theory of action. But observe these same people's behavior, and you will quickly see that this espoused theory has very little to do with how they actually behave."
The way you can determine a smart person's real behavior, not their theory of who they are, is to spend time with them on their failures. Can they describe to you a time they failed? What did it feel like, what lead up to it, what would they do differently? What areas of growth are they still working on improving that hurt them then as well as now? When I look back on the bad hires I've made (and I've made plenty), I can think back to the interview and note that I missed the introspection step.
I'm still surprised when I ask the question "So, tell me about a time you failed and what you did that contributed to the failure", shortly followed by "and what is the area you still need to improve where you keep screwing up and you're currently working to fix?" Some very smart people cannot talk about their failures in a meaningful way, or they give all the reasons why it wasn't their fault. Conversely, it is powerful when a candidate can tell me what they are working on (in personal development) and how they are looking for a team with complementary skills, or an environment where they can grow and learn.
Note, this is not about emotional intelligence (EQ). Being charming in an interview and being the person I'd like to hang out with in a bar is not the same thing as being good at learning with a team.
When measuring intelligence, the first step is to test if the candidate is smart enough for the job you have. Technical tests or emulations of real life situations (e.g. for sales) are necessary to find the high IQ candidates. However, it is just as important to make sure you are hiring someone who can learn as your business changes from failures and difficult circumstances without becoming defensive. Those people will not only continue to improve despite hardships, but they will also drive your whole team forward with their willingness to acknowledge and learn from mistakes.