Background
I'm the DM of a role playing group. Improvised rule set.
I've created a world for my players where I have tried to be as close to 16th century reality as possible, with the additions of magic and phantasmal beasts being extremely rare and stigmatized to even talk about among commoners.
The characters
Two characters are present, a third was playing but had to pause due to becoming a daddy.
Here is a good place to mention that I encouraged my players to write a public story and a private story. There is one part of their background that no one else in the party knows.
First we have an assassin posing as a priestess. Her priestess side was supposed to be a cover, but she has now noticed that she has to actually play an inept priestess 90% of the time and the assassin she wanted to play only gets to come out when she sneaks away from her partner and gets a private session.
In order for her cover to be believable she cannot show that she can stand on her own in a fight, not that she can much, as she is specialized in poisons and sneaking, not combat.
The second character is the son of a jeweler who got down on his luck, lost too much money by gambling and was disowned by his father. Now he lives his life as a vagabond and survives by being very good at bluffing and sleight of hand tricks. He is decent at throwing knives but that does not help him in a stand up fight much.
The problem
In a realistic world, where the main characters are encouraged to do what is really in their characters to do, meaning for the most part, stay out of trouble and be cautious about strange things. How to get the characters to be passionate about going on a perilous, life threatening journey?
What I tried
- Mystical robed figures transporting strong boxes
- A Family on the run from assassins
- A wealthy guild of merchants ripe for a heist
I've told them (per realistic game system expectations) that I will enjoy killing their characters if they do things that are out of character. I've also told them about my trouble of getting them to be curious about things. We all agreed we want to stick to playing realistically though.
The passiveness of the players remains, I could hardly get them to save a tavern owner from local thugs without the help of some NPC muscle.
TLDR Question
What's a good way to motivate realistic, overcautious characters to risk their lives?