In an ideal op-amp, the rules treat the + and - terminals symmetrically, so in principle, it does not matter which terminal is which in this idealization. However, real life op-amps are not ideal, and the inner guts do not treat the inputs symmetrically. Op-amps are designed to work best if the (negative) feedback goes into the negative terminal. (I'm not sure if there's a simple explanation for this, without going into details of op-amp schematics and operation.)