Being pretty sure I'm in the top 90% of society, in terms of intelligence? Does that count for anything?
I'm pretty sure the overwhelming majority of malware infections these days are trojans, typically resulting from users not being able to tell the difference between a local antivirus-software dialog box and a banner advertisement on a website, or from users willing to turn off their brains and do anything asked of them if promised something completely inane and worthless (like a bunch of "smileys" to download) or something way too good to be true (e.g., free trendy twelve-inch smartphone). If you don't do anything *obviously* stupid, I figure your risk of infection is actually quite a bit lower without protection than it would have been with protection twenty years ago, when file viruses were still a thing.
With that said, I do also use a firewall and some other basic precautions. But I consider that stuff secondary. The primary line of defense is just not doing anything incredibly mind-bogglingly stupid.