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Why Are There Software Bugs?

When software operates in a way that is unintended, it might be considered a software bug. Software bugs are beyond frustrating, and from the outside may seem completely avoidable.

Before diving into why there are software bugs, it is important first to understand how software works and why it is inherently complex.

Why Are There Software Bugs?

Why Is Software Complex?

As of yet, computers can’t think. They can’t understand assumptions or implications. This means when you write software, you have to tell the computer exactly what to do in each and every scenario it will ever encounter.

If data is out of bounds or missing, what does the software do? If the database to store the data is no longer available, what does the software do? If a 3rd party system gets modified and is no longer functioning the way it used to, what does the software do?

The only thing it can do is exactly what you programmed it to do. In effect, the programmer has to think of every situation the software will encounter for the next several years, and code the software accordingly.

Why Are There Software Bugs?

What Is the Cause Of Software Bugs?

Software is hand-made. Like when building a house, there are going to be imperfections.

Below are just a few examples of how bugs might occur in software.

  • The requirements are not detailed. For example, the design may have stated that the application should have a contact form, but didn’t state that a particular person or group of individuals should be notified when it was submitted.
  • All possible scenarios were not known or considered in the design.
  • The software is being used in a way that wasn’t originally intended. For example, your software may have been written for college students, but when it is rolled out to high school students, it doesn’t work because the system requires SAT or ACT scores.
  • The software doesn’t know how to handle parameters outside the expected bounds. For example, the software should prevent, or know how to treat a situation where someone tries to order a negative number of an item. Otherwise, you could credit a customer’s credit card unknowingly.
  • The software depends on 3rd party applications that have changed or no longer work as expected.
  • The software works differently on different browsers or different devices or on different hardware.
  • There is a hardware failure, or the hardware becomes temporarily unavailable
  • The software wasn’t designed or written to scale. For example, the application may struggle when the database gets large or there are a lot of users are using the system.
  • The software has not been well-architected, where code is intertwined and one change in one area has a ripple effect to other areas.
  • The software wasn’t written to match the design, and the issues were not found during testing.

As you can see, there is a lot to consider when building well-made software.

Why Are There Software Bugs?

How Can Software Have Less Bugs?

There will always be some bugs in software. This is because it is expensive and time-consuming to test every possible scenario that an application could experience both now and in the future. But that doesn’t mean we don’t try to reduce the number of bugs by applying good design and coding practices.

Below is a list of four recommendations to help reduce bugs.

Write clear requirements

Great software starts with precise requirements. The more detailed you can be about how the system should act in all scenarios, the fewer assumptions the development team will make.

Because every detail of a software program must be coded, strong requirements help your software team help you.

Architect The Software To Last

It is not uncommon for software to change over time, with new functionality and modules being added, and existing ones changed.

Much like building a house, software needs a foundation and structure to keep it’s integrity and accommodate changes in the future. A solid architecture (the way a system is organized)  allows for this to happen.

To avoid bugs related to changes in the future, your software architecture needs to be designed by a skilled team who know how to build systems that will last.  In addition to maintenance and enhancements, a good architecture will also help you to scale as your business grows and your application becomes more heavily used.

Handle Exceptions

Software needs to assume everything that can go wrong, will go wrong. Every time the code relies on something to happen a certain way, additional code needs to check and do something useful if that required condition is not met.

Is the database available? No. Tell the user and ask them to try again or call a support number.

Is someone trying to place an order for a negative amount of items? Give them an error message and ask them to correct the mistake.


How and what to test is a big subject area, and may cover many topics such as automated unit tests, code coverage test, cross-browser compatibility, performance and load testing.

What is important to know is that software must be tested by an experienced person or team that are separate from the development team.

Good software testers know the weak points of a system and will apply pressure to make sure everything works according to plan. Their job is to try to break the application by all creative means they can think of, no matter how unlikely.

Why Are There Software Bugs?


It can be frustrating to have software developed and find that it has bugs. Software is by its nature complex, making bugs a natural part of software development.

Although there are many reasons why bugs happen outside of your team’s control, proactive steps can and should be taken to help keep software issues down to a minimum.

It starts with having an experienced team who knows how to help you capture your requirements, build your application with a solid architecture and then code and test according to best practices.

We want to help every software project begin on solid ground. In The 5 Pillars Of A Successful Software Project we share the five essential ingredients of every software project. You can grab a copy of the guide below and share it with your team!


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