Analytical solutions are usually not available for most geotechnical problems, especially those related to people's daily lives. For applied and research problems, numerical methods and computer programs are needed for both. During the past forty years, many numerical methods have been developed and perfected for various types of engineering problems. Today, engineers are well adapted to use various computer programs to provide solutions to engineering problems. However, there are major problems in recent engineering works, and that is, most engineers are not familiar with the basics of numerical methods, methods of applying them, and the limitations of numerical methods/computer programs. In fact, to a certain extent, the way numerical methods are used and their limitations are related. In many studies using different commercial numerical software, in some cases, the researchers get completely different results with different software or with the same software but different settings for a specific problem, and this is a very common case.