Troubleshooting is an art not a science in any domain. The same symptom may be due to different reasons. If your query is slow, it is can be due to many reasons ranging from hardware to other queries. In this latest article at Sqlshack, it is discussed how to perform troubleshooting in SQL Server using wait stats. In my personal experience, I always start my troubleshooting with Waitstats and it gives us the complete picture as well as it does not cost your system.
Read the article at https://www.sqlshack.com/troubleshooting-using-wait-stats-in-sql-server/
