I owned and used PCs for nearly 20 years without using anti-virus software and was never infected. I actually tried Norton and McAfee over the years, but they caused problems more than anything else. Don't think any installation lasted a week.
But did I finally give in about a year ago and now I run the free version of AVG. I'm able to configure it so that it doesn't get in my way. It has yet to alert me to any viruses. For kicks and giggles I run a scan ever couple of months. I haven't yet, and don't expect, to find anything.