I have a SIMPLE bad mood Mechanic.
We have personalities that make us have a Bad mood as related to our dislikes. If I like Games and dont get to play them I am in a (various degrees of bad) mood.
My likes and Dislikes predict what will get me into a BAD mood.
Every degree of bad mood affects my behavior and decisions.
There are two common strategies (not the only two) - Process it OR Defer it (aka Distract from it). A common Distraction is something Pleasurable - again this depends on my personality what gives me pleasure as well as other Attention shifting strategies.
Then there is PROCESSING it and the most common type of processing is Talking about it, then there is talking about it with oneself in writing, and then there is Reflection and meditation.
Deferring it is FAST and the go-to given most circumstances since we have very Spare or scarce attention. Processing eliminates the Cause and Reshapes the personality but takes the most time and INACCESSIBLE for most people because of a lack of relationships, time, or access to sources.
Lately, I've made any "Disadvantage" or Trait where the character has to behave in a particular way affect their mood and their mood will distract them and change their behavior. They can be hostile, unfriendly, or distracted and troubled.
I found it interesting to Role-play because basically, that's how my personality works.
Stuff that sucks - makes me feel bad. I can either process it or defer it. Most of the time, because of the scarcity of time and knowledge I defer it, most of my personal improvement and change comes from Processing it.
Its like a story where We confront our behavior and our behavior leads us down interesting stories. Stories about who we are and with the opportunity to process we come out of it differently - grown.
Not tackled is the vicious cycle when our bad mood leads us dark paths and we let these bad decisions Define us. That tricky thing about permanent and changeable: Are we changeable? Are we permanently this way? Does bad actions make us Bad People? Or can Good people do bad things?
In the end - Time and Opportunity determine how well we can Process or Defer our Problems.
I basically threw out the GURPS disadvantage control numbers in the game and said: IF you don't act like your character you feel shitty - and you role play being shitty.
And OMG that's so effective - it makes more sense "We do what we do because we are avoiding feeling shitty" (Oversimplified of course).
So even the characters where Players intentionally choose "SAFE Disadvantages" they are STATIC - nothing to PUSH no Issues, no ideals, no beliefs, nothing - the character is NOTHING - our problems - the disadvantages or traits that PUSH us to Action are Important.
These are our FLAWS our FLAWS are us - if a character is Completely STABLE then they are stagnant. They DO NOT ACT! They do not CHANGE! They ATROPHY! they fall into Viscious Cycles!
It makes you realize why in nature there are Humans with Higher Risk Appetites - who like to venture to the Unknown (like my Dad, gamblers, risk takers, Idealists, Scientists, Adventurers etc...).
Psychological Traits will BORE most people, Combining Psychology, Storytelling, and Engineering is not respectable - especially when one argues that our flaws and irrationality is the seed for a Virtuous Cycle - like the first Life - by random accident of nature and its cycles - some bunch of elements got together and began to replicate itself. Our irrationality - the behavior that is sub-optimal - is life and is us changing and making ourselves and others better off.