* Technical failure in a professional setting can lead to loss of your source of income and therefore, in the worst case scenario: loss of access to food, shelter, comfort and other basic life necessities. Failure at a personal project has no such comparable consequences. Techniques to minimize failure are quite literally a matter of survival in a professional context; they are often an afterthought in a personal project. Fault prevention and tolerance are often the most difficult characteristics to achieve in any sufficiently complex software system, and their prioritization or lack thereof has an enormous impact on virtually every aspect of working on such a system.

* In a professional setting, you often have little choice of who you work with. Therefore the technical choices you make in a professional setting must take into account the possibility that the next person who works on your project may be someone who does not understand, like, or care about the way you do things, and that the way they interact with your work may have significant negative repercussions for both you and the project. This is often a tedious, difficult, and time-consuming task that requires different techniques and approaches than one would use when working on a personal project. Conversely, in a professional setting you will also inherit the work of others which may be done in ways you don't understand, like, or care about, with few or no options to change those ways, and you must develop and adopt technical strategies to deal with this as well.

* Documentation, readability, and testing take much more precedence in a professional setting since they serve as guardrails for the long-term integrity of your work as it gets passed on to others to maintain and expand.

* Working with others also requires agreement, and usually mutual compromise, on basic standards, conventions, and processes that can significantly affect your daily workflow and may greatly differ from how you would work on a personal project.

* The end goal of personal projects is usually personal enjoyment, satisfaction, and learning. The end goal of the vast majority of professional projects is to generate revenue, or otherwise serve some need that your employer deems sufficiently important to fulfill by compensating you. The intersection of techniques that are personally appealing to you and the ones that will generate value for your employer may be very small or nonexistent much of the time.

* Your employer may not care about letting technical debt pile up indefinitely as long as you can keep cranking out new features and meeting deadlines, code quality be damned. Alternatively, your employer may impose onerous processes to ensure code quality and integrity that aren't really necessary or effective, and which may even be counterproductive. In fact, there's a good chance your employer will understand very little about what you do at all and make demands that are incongruent with technical realities, which you must deal with, sometimes by performing pointless tasks solely to appease them.

* Personal projects are usually started from scratch, and often dropped or 'completed' once they reach a certain level of complexity, due to the increased level of difficulty brought on by said complexity. Rarely does one have the luxury of dropping projects on a whim for such reasons in a professional context. In general, working in a professional context often involves dealing with a lot more annoying complexity and thorny problems that simply cannot be ignored. Even successful, enjoyable professional projects may become boring after a while since their success will draw continued investment by the employer, oftentimes in areas that are uninteresting or largely irrelevant to the aspects that were originally exciting.