The guilt (and equipment) stacks up like tetris: this is only one of my equipment cabinets; if I don’t put everything in just so, then it won’t fit. And lighting gear, accessories, tripods, bags etc. are stored elsewhere.
Any photographer who tells you that they are a hundred percent, completely indifferent to equipment is lying. It is almost (I say almost to cover myself in the unlikely event there really is somebody out there) impossible to be immune to the lull of new cameras, lenses or accessories; we’ve all felt the pull at one time or another, no matter how weak or irrational. Actually, it’s the irrational that I’m going to talk about today – purchases that are necessary from a professional standpoint (e.g. you have to buy lights if you’re going to be a studio product photographer) don’t really require justification; at least insofar as there are degrees.