In our group, it's a mythical connection with sorcerer levels.
I DM'd a sorcerer who, until 5th level, never took a single point of hit point damage. (He
did take some subdual damage at 2nd level, but that was the Paladin punching him, so it didn't really count.) He finally took some damage when he opened a flask of alchemist's fire and sniffed...
We had a sorcerer in another party who would Mage Armor up at the slightest noise from outside the radius of the torch... who was always cowering at the back... etc, etc.
We had a half-orc barbarian who happily waded into combats with his greatsword... until he levelled up and took a level in sorcerer. And suddenly, he seemed horribly concerned for his own skin, and avoided melee.
And so, ever since then, when a PC starts acting like a wuss, he gets regaled with catcalls and "So - level of sorcerer coming up?"
Most recently, it was our paladin. 20 Strength half-orc. With a pansy longsword-and-shield combo, and never exactly displaying valour, courage, or any of those other paladinly aspects.
We finally sorted it out at a session the player couldn't attend, where the PC was run by committee. He ditched the shield, picked up a greatsword, took point, and solo'd a Bearded Devil (killing it with a greatsword attack from prone, on 0 hit points, having just been CLW'd awake from unconsciousness, and falling unconscious again).
So my suggestion for how to fix a wussy PC? Run a session without the player there, and present him on his return with his New Improved Brave PC as a
fait accompli
-Hyp.