Mistakes or errors are made by software developers during production and cause defects in the software. These defects lead to software failure.
The software has chances of errors as they are manually designed. The errors produce defects or bugs in the software. These defects can be introduced during the coding phase of the software and throughout the development lifecycle.
In the development life cycle, errors can occur at the beginning phase where requirements are understood, written, or designed.
Errors can also result from a mistake while porting the application into production. If the faulty system is executed, it might cause a failure.
However, every mistake does not lead to a defect, neither does every defect lead to a failure. Sometimes, defects lie dormant within the software till they are triggered.