Etymology

From homō ‎(“man”) + ego ‎(“I”) + sum ‎(“I am”) the first person singular of esse ‎(“to be”) and then homō ‎(“man”) + tu ‎(“you”) + es ‎(“you are”) the second person singular of esse ‎(“to be”). Literally "I am a man, you are a man"; from the play Trinummus by Plautus:

Homo ego sum, homo tu es.

Ita me amabit Iuppiter, neque te derisum advenio neque dignum puto.

Verum hoc quod dixi: meus me oravit filius, ut tuam sororem poscerem uxorem sibi.

I am a man, you are a man.

So may Jupiter love me, I have neither come to laugh at you, nor do I think you deserving of it!

But as to what I said, my son begged me to ask for your sister as his wife.

This is somewhat like the like the line by Terence in Heauton Timorumenos; homō sum, hūmānī nihil aliēnum a me putō ‎(“I am a man, nothing that is human do I think unbecoming to me”).