How can I force myself to make eye contact when talking to people?

I’m fairly shy when it comes to talking to people in real life. I’m a social butterfly when it comes to online, texting, etc. Whenever I talk to someone I will not look them in the eyes. I know people take this as me being rude, but I can’t make eye contact with them. I’m scared to look people in the eyes. How can I force myself to look people in the eyes? My friend tells me to count for five seconds, but the moment I look up..I’m looking back down a second later. I hate not making eye contact, but it’s scary and I utterly don’t like doing it. I feel all exposed when I look people in the eyes. I know I have to start doing it eventually, so how can I start? Looking in the mirror doesn’t help. I can’t even look my own self in the eyes. :/ Also, what could cause this?