Why i need decision tree to predict my test data when i'm giving large training data to Train computer? : I'm a student of BSCS, I'm learning data mining. 1 question in mind has totally confused me. If I had made or written my coding for decision tree then why I need Large training data to predict answers of my test data? How training data is helping me when I am checking my each test data line through some lines of codes? Passing them through step by step, if at any step they are not matching my conditions I'm writing no in answer if they are passing all conditions successfully then I'm writing Yes in answer using my code. Now how training data is helping ? if it help computer to predict then why I need my decision tree or model to answer my data??