"Then he is the first sea captain I ever heard of that wouldn't," I asserted confidently.

This has not, however, prevented authors from confidently asserting their opinion:

The days have passed in which Tennyson could confidently assert:

Why do I confidently assert that the dream state is transitory and unreal?

So it can be fairly confidently asserted that the legend is in fact a myth.

We don't have to experience rattlesnake venom to assert confidently that it is toxic if injected.

Don Juan asserted confidently that he had the firm support of numerous followers.

Potter confidently asserted her tales would one day be nursery classics, and part of the process in making them so was marketing strategy.

That's what I like most about Gore: he confidently asserts his assumption of superpower responsibility.

"She's over at Toopy's," he confidently asserted, and started to find out.