Nothing everything in life is self explanatory. There are things that seem to defy reason and fit into the category of "whose every really gonna use that?" Like Geometry.

So many things in life make no sense until one day they do and you realize... you just weren't paying attention. Maybe you were busy or tired or drunk. Anytime you discover the simple stuff has thwarted you, it's embarrassing. 

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Redditor ThatGuyPhillip asked the question... What was your Ohh, so thats what it was for moment that took you too long to find out?  

The answer? Stupidity is universal.

Who really understands their dashboard?

My mom didn't know what the oil change light on the dashboard was. She went to her friend (who did a popular morning talk show in Montreal) and asked "why is there a gravy boat light on my dash?" The next morning the entire city knew she'd said that.   Wonka_Vision

En garde!

Those little green swords at Starbucks. I had no clue what they were used for until I was complaining one day that my coffee gets all over the lid when I walk. My friend grabbed one and stuck it in the top of the lid and asked why I didn't use a stopper. a stopper omg my life has just changed. lifesmell

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Lint is tricky.

Not me but my dad.

He always likes to look nice and put together. One day before church (I was maybe 14), I asked him if he had a lint roller. He got it for me, and it was absolutely covered in lint. So I ripped off the top sheet. Dad's eyes widened in shock. "I always thought lint rollers were so expensive for how few times you could use them!" He never knew there were more sheets underneath. Dad was in his mid fifties then. He hates when I tell that story.   nukethem

Fire detectors are for the Mensa level only. 

Not sure if this is a feature on all smoke detectors, but finally after five years of owning my house and getting used to grabbing a chair and knocking the batteries out of it, I just hit the test button on the front when it went off while cooking. "Hush mode activated". It turns it off for fifteen minutes and automatically turns itself back on. It felt like unlocking a secret character in mortal kombat.  Nebakanezzer

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Teachers are shifty.

When I was in first grade, our teacher had these really cool cookie jars. One was a dog that made barking sounds when you opened it, one was a cat that meowed, etc. We all loved those cookie jars. 

I realized literally yesterday that they make sound so the adults know when someone's getting into the cookie jar. It's genius.   Anonymous7056

Does Ed Sheeran know this?

When I realized that the division sign '' is an empty fraction. HarbingerDe

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One room at a time.

For years I have had this electrical outlet on my back porch that is really intermittent, damn thing works about half the time, then stops working for a couple of weeks. Frustrating. About six years after I bought the house, I also figured out what that one switch in the living room does.   FigurantNoMore

Ugh, men.

You know the plastic hooks on vacuum cleaners that are used to wind the cord around. Well the top hook will spin 180degrees to release the cord, so you don't have to spend time unwinding. Didn't realize this till my wife showed me well into my 30's.  detmeng

Beuller? Hello?

Went into a store and purchased a nice suit for work but forgot to bring the coupon I was going to use. I asked about it while checking out and the girl told me she's sorry but can't help me. She then placed the same coupon on the counter and asked if I had dropped it. I must have been distracted because I denied that it was mine 3 times before I finally understood she was trying to be nice and give me a coupon. Felt really dumb. Dr_Pillowtalk

Do you understand the words coming out of my mouth?

My GF at the time dropped her cellphone into a pot of water. Didn't have water-damage insurance. Did have theft insurance, as the employee pointed out 6 times.

Someone commented with an almost perfect recreation, but I can't find it here. So here it is for your viewing pleasure.

"Sorry, we don't have water insurance. But we have theft insurance."
"Huh?"
"We have theft insurance."
"Yeah but it's water damaged"
"And we have theft insurance, ma'am."
"Yes but--"
"Ma'am. We have T H E F T I N S U R A N C E."
"...I'm confu--"
THEFT INSURANCE. WE HAVE IT. JUST LETTING YOU KNOW IN CASE YOU EVER NEED IT. Such as now".

The-True-Kehlder

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Let the river run.

It took me four years of owning a car to realize I could spray washer fluid onto the rear windshield.

I just assumed it only sprayed the front and I would just occasionally throw a bucket of water on the back if I needed to. Then one day I just noticed an odd symbol on a lever I hadn't seen before. Held that mother down for about 10 seconds before a massive gush of liquid burst out the back and changed my life for the better.   MrAndypong

Take a risk. Push the button.

I bought a used pickup truck in the late 90's that had an electronic key fob like any car these days. It had a couple other buttons as well that when pressed did nothing. I asked about it at the dealership and they told me it was probably for a remote start that wasn't hooked up. After two years of driving that truck around in cold Chicago winters, I sold the truck to my brother when I bought my first new car. One day while talking to him he started the car up with the remote starter. I stared in complete shock as he explained that you have to hold the button down.   LimitedLives

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Protection first. Gloves always.

I was a housekeeper for someone years back when I was in the college (side job, extra money).

I would see short straws in the random places at the house where I worked. I usually just picked them up and threw it in the trash can. It took me two years to realize the person I worked for had drug addiction and he used the straws to snort the drugs. Now look back, I am glad I wear gloves for cleaning other peoples houses.    AmIEnough_4TheWorld

Leave the receipt and instructions.

I had no idea that salad spinners were to dry your salad. I thought they were to mix your salad dressing or some shit.

We got one as a wedding gift, so I loaded one up, dumped some dressing in, and spun a ton of the dressing off of the salad. This made me think the product was to apply dressing flavor to all of your salad bits, without dealing with all the calories that can come from overloading on dressing. So naturally I thought it was a total waste of time and money, and tossed it into a cabinet never to be used again.

A year goes by, and I see a comment on Reddit about salad spinners and how they are such a game changer and so worth it, and I thought people were just batshit insane.

Nope. I'm the idiot here. They're to dry your washed salad bits so you have nice, crisp, not-soggy salad. I had no idea, and the box sure as hell didn't tell me that.   MSDMSMPMCRAPAFRRC

As long as he washed his hands it's cool.

I worked with a guy on a construction site, and it took him 7 months to realize that the porta pottys had urinals in them. He thought that bowl in there was for a sink that they put in the nicer ones.  NotVerySmarts

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All muscle, no brain.

Just today at the Gym: I forgot my shower sandals, and I was like, "oh sweet, they have disposable slippers, just in case such an event." Put them on, walked through the change room, used them. They worked well..... I just realized they were showercaps.   Axle_Goalie

Shut up. Really?

The wiggly metal bracket on the end of a tape measure is like that on purpose. The amount it wiggles matches its thickness. So you can take inside measurements (and push it in) or outside measurements (and pull it out) and you'll get consistent measurements.  tbnrg

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Is that how chickens do it?

That I did not need to put eggs in the refrigerator egg holder one by one. Instead, I could put it on top of the eggs in the case and simply flip it over.  WHL333

Bless his (and your) heart.

My uncle decided to start driving a moped around instead of his car when I was about 6. It dawned on me years later that the decision wasnt exactly voluntary.   rocketman4

H/T : Reddit,ThatGuyPhillip