Noob mistakes

Hello I thought I will create topic to share your most noob moments or form of lack knowledge of game mechanics that u would consider noobish so we can teach each other on our mistakes.
So here we are my mistakes:

• Turns out Koreans war wagons are cavalary archers and not do well against goths ( I thought it counts as siege )

• Khmer Elephant ballista count as siege so died easy to onagers

• chemistry adds 1 dmg to archers ( I thought it only unlock gunpowder units)

So here are my examples, yes we all die to boar or vile TC but I was thinking about more mechanics or game knowledge mistakes.

Please share your thoughts :)