How to Decide if You Should Buy Something as if You Were an Operative

If you need to buy food or pay for bills, you don't really need to contemplate if you should or shouldn't spend your money on it because the answer is you should. This is for those other times.

If you need to purchase something like sustenance or pay for bills, you don't really need to decide or contemplate if you should or shouldn't spend your money on it because the answer is you should. This is for those other times.

By one definition, from my experience and past profession, I am a "security expert".  Specifically, an expert on breaking / bypassing physical security measures implemented by an opposing foe or neutral target.

From this, I came up with the "The 3 Operative Laws of Physical Security". In short it theorizes that any security measure is bound by time, effort and force. That all security measures have a finite amount of time before exerted force and effort against it will break it. The trick is calculating how much time will it take to break the security using how much effort and with what force. This was the basic formula I used to see if a certain security measure was worth engaging.

How does this relate to deciding on if I should buy something?