What am I?: A Riddle

I’m everything

I could be nothing 

My value is determined when you act

Forever bluffing.

A light at night, or 

A cloud overhead

Your disposition aims my direction 

You decide what’s said.

All that could be, and 

Even some that won’t

Do your worst, but you will never reach me.

But, measure me? Don’t.

I court hopes and dreams

I crush weak spirits

I’m perceived best by those whom I’ve deceived

Vague to those nearest

Everything and 

Nothing are only

My limits, for when you ascend or fall

You leave me lonely