1. Can I Afford it?
If I need to borrow money to do it -- I probably can't afford it.
There are exceptions of course. Some people would argue that education and housing loans are necessary. But even then, I would think long and hard before signing up for long-term debt. As much as possible, I will only commit to things I can pay for immediately.
I say this while recognizing that some people are already too deep into poverty to escape -- without external help.
But for most of us non-poverty-line people -- learning to live below our means would remove a lot of stress from our lives.