It is important to address the full SLC as differentiated from the Software Development Life Cycle (SDLC) because too many programmers (coders) think the SDLC starts when someone else gives them the system requirements and ends with delivery of the code to meet those requirements. The complete SLC starts with the process to develop those requirements and continues through the operations, maintenance, and retirement stages of the systems' life. Especially in the world of security, paying attention to the security at retirement (e.g. disposal, destruction, data preservation, etc.) is a crucial part of our jobs.
Good luck, and congratulations on deciding to dive into a most important part of our profession.