Well, sometimes you can fall into that really big sin which once plagued you. You thought you were over that one, huh? Maybe you were too mature to fall that way again? Sometimes great big falls from grace happen, so that after our repentance we become even more humble. Sometimes our falls serve to wake us from our complacency, presumption and self-satisfaction. The experience can be valuable to demonstrate just how much we need God - or owe God - and thus we are reminded that we can do nothing good without Him. Of course, sometimes we've just been in denial about our intentions and desires... concupiscence - ignoring the occasions of sin we place ourselves in.
But what if you really are doing well, and you just aren't plagued with temptations, and no occasion or near occasion of sin seems to be hounding you? What if you are making it to Mass, setting aside time for prayer and everything is good? Like you are just not bothered any longer. What up with that?
Many persons who find no sin in themselves, because they have committed no grievous sins, are full of sins of omission, sins of indirectly voluntary and consequently culpable negligence. - Garrigou-Lagrange*Another reason for big falls may be attributed to our negligence in regulating venial sin. In addition to that, sometimes after we've struggled with habitual mortal sin for many years - we can be so focused upon the serious stuff, we just don't notice the venial sins and imperfections which have attached and cling to us.
Disclaimer: This post wasn't about anyone in particular.