Simplest answer goes by the famous proverb: "To Err is Human & to Forgive Divine". Every software is created by Human beings, but here Divine is not going to forgive the software creators for their faults or the faults in the process. When defective software goes out to the customers, It is the Software Selling Company who pays out of loss of revenues accrued due to dissatisfied customers. Number of dissatisfied customers keep on escalating unless immediate corrective measures are taken & customers are made absolutely satisfied. No clients will be satisfied with you unless you are producing defect free applications.
It is understandable that the Development Process is not always able to produce defect free software product. Even if the Development Process is absolutely good & foolproof & produces Bug free software; we cannot be certain about it unless & until we test it. Without testing the outcome, no software producing company will have an iota of confidence on the correctness of the product,
What is the main cause of bugs in software application
Inadequate understanding about the requirements.
Improper translation of the design to the actual code.
Absence of proper unit testing.
Action Plan to reduce the Bugs or Defects in software Product
1.Capture, Record & Transmit the Customer needs more precisely.
2.Direct the efforts towards making the development process consistent
3.Strive to detect the Bugs at every stage of the product development during its life cycle.