"I have 22 years of experience in the area of woodworking, and I always had a huge difficulty when starting a new project: choosing a tool. Do I need a chisel?

"I have 22 years of experience in the area of woodworking, and I always had a huge difficulty when starting a new project: choosing a tool. Do I need a chisel? Or a hammer? Or should I go for a screwdriver?" Databases are tools like any others, and you choose them based on what you actually need for any specific time. In fact, many projects already use multiple databases - storing dynamic state in a RDBM, and static resources in the filesystem (which is absolutely a database). Of course, there are other criteria involved, like e.g. the familiarity of the team with different database paradigms, but the core fact stays the same: database is a means to an end, which can be summarized as "finding a solution for persistent storage of some data".