“Make the character vulnerable” is good advice that tells you nothing about what to actually write.

So here’s the specific menu of losses. A character becomes vulnerable through the loss of something. Name the loss, and you’ve found your scene:

Jeopardy — loss of physical safety
Terror — loss of emotional security
Horror — loss of hope
Neglect — loss of care
Loneliness — loss of companionship
Unfairness — loss of impartiality
Injustice — loss of justice
Rejection — loss of acceptance
Abandonment — loss of connection
Humiliation — loss of status
Frustration — loss of purpose
Insecurity — loss of stability
Misunderstanding — loss of communication
Not being believed when telling the truth — loss of trust

Andrew Cooper in Your Friends & Neighbors runs the whole gauntlet in one pilot: humiliation (fired), abandonment (divorced), insecurity (broke), rejection (frozen out of his own life). We follow a man committing burglary because the writers stacked his losses until we couldn’t look away.

When a scene feels flat, ask: what is this character actually losing here? If the answer is “nothing,” that’s your problem.