Being a Senior Developer is more than being a long serving developer
Like many people, I started my development career from another role. I taught myself coding and then built software to help the business and myself. It was well received, but I did not feel like a "real" developer yet. This experience convinced me that software was what I wanted to do, so I looked for a junior developer role. This wasn't easy, most companies want people who can come in and start being productive right away, and there were many skills I lacked from not working in a "true" software development environment. Eventually, after much persistence, I was taken in as a junior developer for a large finance company. When handing in my resignation to my non-dev-shop company, I was offered a pay rise to more than I would be getting in the new role at the finance company. I was also offered a new position, the position of "Senior" developer. Now I had a choice. I could stay, and drive development projects, leading a team of newly hir