I have no idea why, but convention. And not a thing where nerds like me gather to dork out about something, but a scientific standard. Whenever I'm explaining something, and someone asks why it operates that way, I'm always like, "it's that way by.... uh... y'know, it's always been that way." No clue why I always blank on that word specifically.
I had to look it up for this post. My brain's inability to recall the word for detonation velocities lower than the speed of sound wasn't an issue until rotating detonation engines started to make news and I've needed to explain the difference between explosions and deflagrations to people.
I'm better at writing than talking because it takes me so long to think of so many words.
today I paused for 30 seconds trying to remember "second line of defense,"
and paused again for a really long time trying to remember what this thing is called I plug my phone into recharge when I'm traveling, oh yeah it's called a "power bank."
I am very thesaurus-minded and express myself precisely when possible, so I don't have any words I just forget, but once in a while I might not be able to find a word that embodies what I'm trying to get across, which is always frustrating as someone whose first language does have an equivalent to the missing word in question.