Have you ever met someone for the first time and immediately thought they had a great personality? Then you meet them for a second time in a different setting and you have a few choice words you might say about that individual?
That is exactly why more than one interview is necessary in the hiring process. First round interviews should focus on the candidate's skills, abilities and first impressions on their personality. The second interview should take a deeper dive into their skills and thought processes, but also a deeper look into their personality and inherent traits.
If you are hiring for a critical position in the organization, I recommend at least three interviews along with several interviewers.
The more comfortable a candidate is during the interview the better they can express their abilities and the more their true personality comes through. A second interview typically has a candidate more relaxed, as they have already spoken with you.
In the second interview, change up the settings. If the first interview was in the office, perhaps walk the candidate around the facilities or take them to lunch the second time around.
The second interview is not just beneficial to you. For the candidate, a second interview gives them time after the first interview to digest all the information you gave them about the position and your organization. They most likely will come to the second interview with more questions about the role or the company. It gives them time to look at the organization again to see if they feel they would be a fit there.
After all, a good hire has to be a good fit for both you and the candidate. If the candidate accepts and realizes later it is not a fit for them, then you have wasted all that time. Life can get hectic, especially on the farm, but my advice is, take time for that second look, and perhaps even a third.