The hiring manager was emphatic, "If they don't send a Thank You note after the interview, they're not going to be invited back for a second interview." My conversation that day with another hiring manager in the same organization went quite differently. He didn't give a fig about Thank You notes. His hot button was intensive research, "If they haven't prepared for the interview by looking beyond our website, they are not who I am looking for." The second manager expected each candidate to have spent about three hours on research, and he expected that they would walk in with at least 15 thought provoking questions that demonstrated an understanding of both the industry and the organization.
If an organization hires you, you will be spending about 2,000 hours a year with them. But they'll only interview you for about 4 hours (if that). So during the interview process, they are paying 500 times more attention to little things--things that won't matter nearly as much after you start work. You'll really be under the microscope in every interaction. So you simply must be more meticulous keeping track of the little things--all the little things--because you never know what their hot button issue is going to be.
"Duh! Of course I'll do that!" you say. But consider this idiotically simple list below:
Did your resume or cover letter have any mistakes?
Were you on time and prepared for the phone interview?
Were you on time and dressed appropriately for the interview?
Did you prepare for the interview properly?
Were you ready for their interview questions, and did you have relevant experiences you could confidently share?
Did you ask smart questions during the interview?
Did you send a Thank You note to everyone you met?
Did you send references or other follow-up material in a timely manner?
Obvious and idiotically simple, right? Except at least a third of candidates routinely fail to do this. That's because what it takes to keep a job is quite different than what it takes to land a new one.