You learn about wrenching the hard way sometimes....funny story about my beginnings in mechanics with my Dad (he's gone now)...
When I was around 14-15, I was "helping" to change the oil in my Dad's '56 Cadillac. My job was to drain the oil, so I went under the car and drained it...and as was the case with things in the '60's, I carried the oil to a nearby field and dumped it (all the environmental things were different in those days).
After that I returned to tell him that I was done...and he then poured in the new oil while I watched. (ah, those wonderful father/son moments

....anyway, soon he decides to start the car and drive it, but it won't move (he really wasn't much of a mechanic, but he tried). This puts him into a panic and he starts calling his different mechanic friends. They give him all kinds of advice and things to check....the big question was "why won't the car move after changing the oil?" And finally someone asks him "which oil?"....
Did everyone know that the '56 Cadillac had a drain plug on the transmission pan?
Yep. That's how I got started