Documenting lessons learned is the last step of the troubleshooting methodology, which is a systematic approach to solving problems. Documenting lessons learned involves recording the problem, the solution, and the process that was followed to resolve the problem. This can help prevent future occurrences of the same or similar problems, improve the troubleshooting skills of the technician, and provide a reference for other technicians who may encounter the same or similar problems. Documenting lessons learned would be the next troubleshooting step the technician should do after verifying full system functionality. Determining if anything has changed, establishing a theory of probable cause, and duplicating the problem are not steps that follow verifying full system functionality in the troubleshooting methodology. Reference: CompTIA IT Fundamentals+ Study Guide: Exam FC0-U61, Second Edition, Chapter 9: Troubleshooting and Operational Procedures, page 341.