What’s a small, harmless superstition or belief that you have?

Thou shalt not deploy anything to production on a Friday.

Good one!
Same with making quality or engineering changes in a friday. It's just dumb.
Nothing better than coming in Monday only to have to perform containment of all the bad parts produced over the weekend.
Actually, in some industries this is actually a good thing
If you can have a bumpy first day on Friday, and e.g. the warehouse is closed on the weekend, you can fix all the things you've seen on Friday during the weekend. And don't have to suffer through a real rough week with in-production patching
- you can fix all the things you've seen on Friday during the weekend
  Just how I love spending my weekends.
- True, and I've worked in corp IT for retail and we did actually do updates to the system on Fridays (or sometimes Saturdays) for exactly that reason.
  So it's more a rule-of-thumb than a prime directive, I guess lol.
The queue/phones/inbox/whatever sure is quiet today.
- Back when I was in the helpdesk trenches, the phone system did go out during business hours one time. Most relaxing day of my professional career.

I have a ram pendant so Satan protects me.
I do not believe in Satan.

Never put shoes on a table, mostly just because it's dirty but I think it's something to do with bad luck?

Edit: fat thumbs

The overwhelming majority of people are paid actors whose job is to stand in my way when I want to go home after work.

It’s about harmless beliefs, not not being crazy.

I must clench and unclench my toes a few times on a carpet at the next available opportunity after landing from a flight

I never saw a Unicorn before I believed in them. I guess they have a magical defense against being seen by people who don't believe in them.

Now that I do believe in them...I still haven't seen one. I guess they're not local to my area.

I intend to continue to believe in them for the foreseeable future while I do some travel... just in case.

IMO there are no harmless ones (by that I mean dictionary definition superstitions - not just things like traditions and adages that have a logical reason or basis), if a person truly believes in actual magical thinking no matter how silly it's a doorway to accepting the rest.

Like letting in bullshit like horoscopes, homeopathy, faith healing, yearning for eschatological prophecies...

I feel like bad things will happen to me if I eat a broken butterfinger bar.

If I've been a good boy my poop session will go smoothly. If I think I was a good boy, but then my poop is awful, I think "damn I must have done something...". If I have been an asshole, but my poop goes well, I think "wow, I'm gonna have to pay this back tenfold tomorrow!"

If you hand someone a sharp object like a knife or scissors you will soon get into an argument. Gotta set it on the table for them to retrieve instead.

That's a really good superstition. Everybody wins.

If someone says something bad, knock on wood. Like "Well X thing could happen" where X is like. A storm, the cats learning how to tap dance, a river exploding. Knocking on wood to make that not happen.

Whenever I get out of my car with lights still on and it dings to warn me, I thank it for reminding me. I just know the day I don't do that is the last day that ding will happen!

Salute a single magpie to ward off bad luck

I do a monthly newsletter at work. I collect the stuff for the newsletter in an Excel sheet. I normally end up with around 12 items or so. But that makes my Excel sheet stop on line 13 because of the header row. So I'll add 2 more things. Because if I just add 1 then it will be 13 entries. So my newsletter will have less than 11 or more than 14 entries. I don't know why, I don't care about the number 13 anywhere else in my life.

If I see my initials in a car rego plate I take it as a good sign.

It's bad luck to rest your chopsticks inside the bowl.

Never leave your chopsticks sticking into a bowl of rice.
Always fold robes (and similar) left-over-right.

I don't have good luck, nor bad luck... just wild luck. Not as fun as I would like to believe

When I hang my clothes up on the line to dry, I have to use matching coloured pegs for each item of clothing. I like the symmetry. It feels wrong to do it otherwise.