This was something incredibly powerful for me. The Ramban holds in emunah ubitachon (perek 1), that one may even have bitachon if he is a rasha. Yup.. he says it straight out. That is the reason why it says Bitach BaHashem, V'aseh Tov.

First, Bitcah BaHashem-  every one may have bitachon in Hashem, that he loves them and will do everything to give them the best joy possible in this world. We may rely on this. EVEN a RASHA  he says it out clear as day. 

Second- Aseh Tov.. Secondary to this we must do good. 

Now for one to use this as a rationalization to sin their life away and say they still have bitachin... sounds like they are cheating the system. To that I say- try.. because it's really not possible to do so continuously.. eventually the good wins out if you really believe it. (allow yourself to believe it) Because deep down we all want to be good. 

see it inside for yourself...