It depends on the type of spell. If its a good luck spell, the backfire would be bad luck. If its a spell to cause a person misery or pain, its backfire would be it affecting you and not the person originally targeted.
Normally a spell would backfire if the caster does not have the will power to control the spell.
A spell coming back to you or what have you is a personal belief. I wouldn't know because I don't believe in such things, but in such cases I would normally assume you would see signs. Or kind of get feelings of the spell not working and so on.
My spell backfired it made things worse. One was a binding spell to keep someone from physically emotionally hurting me. The other was a spell to convince to give back to me what they took.this did nothing. Trying to figure out what I did wrong.
Well, I think I got backfired after casting 3 spells for someone i cared about and dreaming them the same night of each spell, but nothing else has happened yet.. the distance between us has increased.
Lately I have started to cast a " come back to me" spell to my ex using 2 rags, a thread and a needle and saying a chant and I have dreamt of my ex the first time I did cast this spell.. hope it's a good sign.