Not explaining your thought process is one of the most frustrating things for an interviewer. Interviewers want to understand how applicants approach and solve problems to evaluate their problem solving skills and determine if they will be successful in different roles. Applicants should think out loud as they work through problems and explain their thought process, even if they get the right answer, so interviewers can understand their approach. Asking clarifying questions, explaining assumptions, and saying "I don't know" when unsure are important parts of demonstrating problem solving skills to interviewers.