It's not stupid.
By itself, RAM doesn't affect computer life, all other things being equal. Truth is, however, that all things aren't equal. If you don't have enough RAM to run your applications, your system can go into "paging", trying to use the hard disk for virtual memory. It's often called thrashing, where the computer keeps reading and writing to the hard disk. It's not a really good thing for the hard drive, and in theory can stress the drive.
I don't know what you've got, but a MacBook running OS X 10.4, for instance, can run on 512M of RAM but does better typically on 1GB. 2GB is useful if you run lots of memory hungry applications at the same time, but isn't particularly necessary if you're not using all of the RAM at the same time.
Hope this helps!