NoSQL is a tool, and like any tool is has specific use cases where it excels, and use cases where some other tool would be a better fit. No one would use a screwdriver to pound in a nail. It's possible, but using a hammer would make the job easier. One large problem with NoSQL databases is that people adopt them when an RDBMS would solve the problem just as well or better.
To understand which tool to be used when, we must understand the strengths and weaknesses of both systems.
One of the biggest strengths of an RDBMS is its maturity. The technology behind an RDBMS has existed for over 40 years and is based on the solid theory of relational algebra and relational calculus. Because of their maturity, they have a long, proven track record across many different industries of handling data in a safe and secure way.