Not being able to select my unit as spefic unit event from variable...

I looked over the campaign maps to see how they did some unit triggers... Often they have... for example

Variable

Majev, Variable type: Unit, initial value: No unit

And when you select spefic unit event, your able to use that variable from the selection...
So I did this in my map

Variable

Fortress, Variable type: unit, initial value: No unit

and I cannot select this variable when I am in spefic unit event... why the hell not?

never mind, Im stupid. It doesn't work on the campaign map either, I noticed the Majev was not the variable, but the actual unit.