Why do some people frequently get called for jury duty while others NEVER get called?

I have NEVER gotten called for jury duty. Neither has my husband or best friend. We are all registered voters. Homeowners. Tax payers.... I don't get it. Some people get called every couple of years like clockwork. Is it random? Or are we not in the jury pool for some reason? My best friend's husband is on his 4th or 5th call now and she's on zero.