There is one vital word that should be on repeat in your writerly brain whether you plot or pants, whether you are writing the protagonist, antagonist, or villain. A word you need to have the answer to fairly early on unless you are okay with massive and repeated rewrites.
Why are your main characters in love? Do they have common goals and interests? Do they have similar backgrounds? What is the driving force making them want to be with each other? If you say lust I may bop you with a wet noodle because while physical attraction and sex are important (especially hot, steamy, kinky sex scenes that you will ABSOLUTELY share with me) they are NOT the basis for a relationship in real life or between the pages of a book. You know this, I know this, let’s move on.
Why does your detective need to solve this crime? Is it a serial killer that needs to be stopped? Was his or her family affected in some way?
Let’s flip it to the dark side. Why does your villain do what they do? Why do they have it out for the protagonist? What is their history? And, believe this or not, what makes them human? I know, I know, it feels good to hate the bad guy, but even they need to have some redeeming qualities. Something to humanize them. Hey, even take it as far as to make our hearts bleed in a way that we feel conflicted about hating them. I mean we still DO loathe and despise buuuuuuut…
What I am getting at here is motivation. Readers need a WHY, whether for the good guys or evil ones. Being “born this way” only works if you’re Lady Gaga. For depth and meaning, there needs to be a connection point between the audience and the character and motivation is a key point in obtaining that. We need to know and FEEL their driving force.
Putting this practically, how unsatisfying is it to watch a true crime show only to get to the end and know the WHO, but not the WHY? Be it a convicted killer who refuses to speak or one whose life ended before they confessed. Either way, it just leaves a big, gaping hole and you realize you just wasted three thousand, six hundred seconds watching something that didn’t satisfy your craving for justice because in some ways there is none without that explanation.
Don’t let your story leave your readers with a bad taste. Be an author they can trust to answer all their questions and leave them content, if not happy.