Why are simple words so hard to spell?

So...just a few minutes ago I got done with playing "Hangman" with Ellen's brother, Noah. Little Jonny also got in the game...and to start out, I started with a simple word. I thought for sure that it would take them no time at all to get it...not so. I even gave them clues...still, the poor hangman had his full body, eyes, a mouth..no nose, three hairs and a few fingers before they finally guessed the right letter...and then they were mortified with how simple it was. Care to know the word?
Hello.
Thats it.
Hello.
And it took them such a long time to finally get it! I was laughing so hard while they guessed letters like V, W, Y...I thought it quite funny. And then Noah did me...I will not lie and say that I had the word in just a couple moments, not so. It took me a good amount of time to get it...and then Noah accidently told me and he filled in the words for me...just as I got it. So it was fun...
And then I did it again with just Noah. I looked around the room and saw a word that was simple, but would be hard to figure out. Platform. Yeah, I know, not like Hello at all. But still...he finally got it after there was only one more letter left to go and he could not get it... I told Noah to look around the room we were in and told him to look for big, white, bold letters. He found it within seconds, jumping up and down and yelling, "F! F! It's F!".
Ah....I just had to write it down...I thought that it was interesting that one of the simplest words took two very intelligent young boys so long to finally figure out...hehe! but I had a lot of fun doing it and driving them all nuts.
Much Luv
Jenna