When you know you know, and you know everyone else has no idea, and they think they do. Often everyone thinks their opinion about the things other's know is definitive and revelatory... but OFTEN... we'd all be wrong. Never assume you know better because you've graduated the school of "Wikipedia!"

Redditor u/cantbelieveitworked wanted those who know their fields as well as they do to share some a few "common sense" duhs with the rest of us by asking.... What is common knowledge in your field, but if you told us, we would think your next level smart?



Bridges aren't fixed at both sides, they're traditionally pinned on one side (with two big super-pins), and just rest unfixed at the other end. This helps avoid additional stress as the bridge flexes during use and expands/contracts with temperature change. HighTide49


Most hacking is about tricking the user, not the computer. thekingofbeans42

This. If I had a dollar for every time I've heard "My credit card got hacked!" I could retire early. No, your credit card didn't get hacked. You got hacked when you gave your credit card to a stranger with a heavy accent because they told you they could lower all your interest rates to zero percent. jmanpc

Fly High. 

Aircraft structural engineer here.

Every airplane you've ever flown on or ever will fly on has cracks in the structure all over the place. It's very very common. And to add insult to injury, if an exterior crack or hole is found that could compromise the integrity of some non critical area like the leading edge of the vertical stabilizer or some piece of engine housing, the standard procedure is to just put some fancy duct tape over it until they can get it in a maintenance hanger.

Oh and also in my personal experience every aircraft is also probably missing about 20 or so fasteners or screws without anyone knowing.

(But on the bright side so nobody freaks out, aircraft are also commonly way over engineered with several backup structures so no one failure can down a plane without another failure somewhere else.) silent_hvalross

Budweiser Flowers. 

When buying roses for someone, give the head a gentle squeeze-if it's fresh it will be firm. If it's squishy, it's no good.

Don't get married near Valentine's Day or Mother's Day. The flowers will be twice as expensive and twice as crappy.

Lastly, florists don't jack up the prices on red roses on v-day to mess with you. Our wholesalers raise the prices because they have to put so much energy into growing red roses that will bloom at the right time. We never really use them except v-day and maybe Christmas. So it's really all the people out there ordering red roses that are driving up the price. I hate them personally. Red roses are like the Budweiser of flowers. Get your sweetie a shit load of tulips, or better yet a live plant. And baby's breath smells like cat piss and dirty socks. Ask for wax flower, it smells like lemons. NormanVename

An Easy Pick.


It's actually super easy to pick most locks used on homes. I could teach a complete novice the basics in 15 minutes. It's a scary thought, but on the other hand that means more people are being law abiding citizens and not breaking into your home. copnonymous

Pain Bock. 

The nerves in your body responsible for conveying touch sensory information conduct a current faster than the ones that are responsible for pain signals. As a result, we believe that the reason a sore spot feels better when you rub it is because the signal from your touch beats the pain signal back to your central nervous system and thus "blocks out" pain. TokenStraightFriend


A urinary tract infection can cause mental health issues to intensify. FormerlyKnownAsKing

Just for people curious, any systemic infection can induce delirium. One of the things ER docs do when there's new onset altered mental status is examine for common causes of infection (lungs, urinary tract, abdomen).

UTI causing acutely altered mental status is common in the elderly, they often can have UTI's with no symptoms or even fever. Fortyozslushie

No Storage. 

Applications with login don't actually store your password directly. If they are able to show you your password or send it by mail it is not safe.

What safe websites do instead is use a method called salting and hashing. This means doing a 1 way scrambling of your password and then save the scrambled value. When you try to login they take what you wrote in the password field and run it through the same scrambler. If this matches the stored password it means you typed in the correct password. This way if they get hacked or people get access to the database the stored passwords are useless.

Super trivial knowledge in programming and IT but most people I've talking to about this outside work have no idea. BigSwooney

Expand the Jaw. 

If you're getting bit by someone, quickly push or jerk the part of you that is being bitten in the direction of the bite and pull back. The push back expands the jaw causing them to release for a second so you can pull yourself out of the bite. sadgrly

Jab and Duck.


How to jab someone with a needle without it hurting (at least for blood draws).

(it's about the angle, the needle has an angled point and so if you match the needle angle correctly with the vein/skin it barely hurts or not at all). Viktor_Korobov


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