This quote means that success is the result of attention to lots of small details. It is based on the idea that when many small things are done correctly, it adds up to create success. For example, if you are trying to build a very large building, success will come from paying attention to the details of each individual component of the project. From making sure the correct materials are being used, to staying on schedule, to making sure that safety guidelines are followed, all of the details must be taken care of in order for the project to be a successful one.