I am eternally grateful to the headmaster at my prep school who explained a big mystery to me. By the age of 10 I knew the mechanics of what was supposed to happen but I couldn't understand how I was going to get this little pink, wrinkled, rather smelly, floppy sausage inside a lady's front bottom. I agonised about it, imagining it would be like trying to stuff a marshmallow into a piggy bank.
Then one day near the end of summer term at the school our headmaster, one Caspar Tremlett Esq. sat us down for a 2 hour French class and cleared his throat then announced that instead of French we were going to have "the facts of life".
With difficulty and clear embarrassment he began: "Now... you boys all have a...... penis. And when you're not using it for urinating, you can be using it for..... making babies..." He then went on to explain the mechanics. I will never forget the wave of immense relief that flooded over me as I understood that THAT was the reason why it was always stiff in the morning and increasingly often during the day too. Being a budding mechanic I could see the structural advantage of stiffness straight away. Bless him, I have never forgotten that insight and how it relieved my worry.