I'd even less like to hear him say, "I don't believe I can fly this plane".
Okay, this example equates "belief" with a confidence factor of less than 100%. In my line of work, we deal with probabilities. We might design a test to show that we can be 60% confident that a computer part will have an annual failure rate of less than a certain percentage. Sometimes knowing something with 60% confidence is the best we can do with the time and resources we have. Sometimes we can "know" with > 99.7% confidence. And sometimes we can "know" with 99.9997% (six-sigma") confidence that something is true, which is about as close to dead-certainty as we can get.
Life is about making important decisions with insufficient data.
However, I'm more intrigued about something you said to Ziggy about "belief" (a mental process) being separate from what you can see, hear, feel, taste, and smell. Then, how do you process the data being input from your senses?