He was unsure of his abilities to complete the task.
unsure about
Frequency:
70
%
She was unsure about the decision she had to make.
unsure how
Frequency:
60
%
I am unsure how to proceed with this project.
unsure whether
Frequency:
50
%
She was unsure whether she should attend the event.
unsure why
Frequency:
40
%
He was unsure why she had acted that way.
Idiomatic Expressions for unsure
Phrase: playing it by ear
Meaning: making decisions as you go along, without a plan
Usage: I'm not sure what time we'll leave, so we'll just have to play it by ear.