Over the last six or seven years, I've found myself having to be an 'expert' on a large range of topics that I had never thought I would need to know. Here's a list (in no particular order) of all the things that I can remember having to be an expert on:

• Accounting
• Carbon trading
• Dental nursing
• Fijian resorts
• Customer management
• Medical equipment
• Carbon certificate reconciliation
• Architecture
• Student examination
• International flight paths
• Warehouse management
• Stock markets
• E-commerce
• News publishing
• Supermarket registers
• Time tracking
• Invoice management
• Multinational corporation office hierarchies
• Community building
• Storing medical records
• Hens nights
• Commercial printers

Pretty varied experience, and this isn't anywhere close to covering all of the projects that I've ever worked on. So am I really an expert on all of these things?

Well no, not really. But while I was working on each project I had to become an expert. I had to understand the rules and the limitations (both physical and legal) for each of these subject matters. I had to build software which correctly performed the tasks required to assist people working in all of those sectors. I had to be able to intelligently discuss the topic with the client in order to build software which would work how they need it to.

I couldn't just write some code, and leave it at that. I had to understand how things worked in order to ensure that my code wasn't going to cause problems. I had to understand the subject matter so that I could foresee problems, and solve them. I had to know it inside and out. For all intents and purposes, I was an expert on every single one of those topics (and many, many more).

There's no great insight here; just remembrance of the topics I was once an 'expert' on. This is one of the reasons why I love being a programmer - I get to learn about so many other professions, become an expert, and then move on. How many other professions get to do that?