Many fathers are a mystery. Father’s Day is often used by Time Travelers to go back in time, and learn more about their own fathers. Watching your dad nervously hold you as a baby, or harshly interrogate your prom date while you are upstairs teasing your feathered hair are are priceless moments that beg to be explored. It is also tempting to try to make little adjustments. Maybe you will even get him to say “I love you” this time around. That would be great! But maybe you won’t….

Here are some things you might want to keep in mind when you visit your dad:

Father’s Day is not for vengeance.

Great catharsis can be found in going back in time and yelling at your dad. Dr. Henrietta May has built a career around it. But keep in mind if you succeed in illuminating your father about just what a terrible job he has done before he has done it, he may not do such a terrible job at all. You could spawn a whole timeline with a much better dad and a you that travels back to the same branching point and wants to know why you’re yelling at dad.

Things may not be how you remember, or what you were told.

You may remember your dad as an overworked provider, only to travel back and find him in a phone booth at a Hooters, telling your mom he has to work late. Or you could sit in the stands behind him at your little league game while you play second base and find that between yelling “Atta Boy”, he is muttering words like like “disappointment” and “faggy”. You might find your dad in line for Star Trek II and be troubled to find the cheap-looking Vulcan girl he is with isn’t your mother… or that she is.

Also keep in mind the ‘Objects in Mirror’ effect. Your dad may not seem as tall, as funny, or even as frightening as you remember. That kind of disappointment sticks with you.

You might accidentally kill him.

Killing your dad is a terrible way to celebrate Father’s Day.

You might prepare for weeks to find your dad at Jeffrey’s Bay so you can surf with him in his prime, only to distract him when that big wave comes. You could simply give him a heart attack when we realizes you are from the future.

You won’t pop out of existence, though you will create a timeline in which you will never be. Your mom won’t be happy about that. Or worse, she will, and you’ll have to deal with a “Reverse Stewart” in which you realize things really would be better if you’d never been born.

Your kid might be trying to visit you.

While you pop back on Father’s Day to visit your dad on a Father’s Day long ago, one or more of your kids might be trying to visit you. Try to keep the ironic time travel to a minimum.