How the hell did not know that for so long moments?

What are some things which made you say "WTH! How did not know that for so long? "

I am talking about things you did not know even after knowing about build orders, strategies, etc and then, like, whaaaat! Here is my list...

1. Scorpios have 0 melee damage and a bonus against Rams... I learnt this the hard way when my Ram train was whittled down very quickly by enemy scorpions... I mean, I knew about Chuks by then... But still, did not know about Scorps...

2. Conquistadors have a base armour of 2/2 and are affected by Blacksmith armour upgrades... Did not know that for a long time despite being my fav unique unit... It was a pleasant surprise, though...

3. Scouts/Eagles against monks...

4. Celts do not get Arbalests ( Please don't judge me)...