Rent a tool or buy it? Where do you draw the line?

[Mike Ross]

Hey BP,
    I'm out here trying a "flip-in" and know I am not looking to become a full time contractor at any point. When fixing things up I often struggle with buying it vs borrowing the tool from home depot. Many things I will only use once, but when borrowing them the savings is only there if I can get the project done in a day or two max. 
   Where do you draw the line? Or, do you just buy it because you never know when you will need it in the future? Just curious if others struggle with this, and how they decide what's worth it, and what isn't.

[Rocky V.]

I love tools so I buy them.  Tools used once a year I typically purchase at Harbor Freight.