Rust is cancer for plain carbon and many alloyed steels. Your geographic location and the climate where your tools are stored will have a lot to do with how quickly the cancer spreads.
The good news is that we are living in an era where there are a lot of ways to protect against rust, and even convert rust to a passive material if needed.
I am a Metallurgical Engineer by profession, which is not any attempt to impress anyone, but to be clear that I work with and try to understand the behavior of metals on a daily basis.
There are a lot of good rust-proofing techniques available, some simple, and some sophisticated. Something as common as plain old WD-40 is hard to beat from a cost-to-performance basis.