The Greek verb diabebaioomai means 'to affirm strongly,' 'to assert confidently,' or 'to speak with firm conviction.' It appears twice in the New Testament (1 Timothy 1:7 and Titus 3:8), both times in the context of what teachers should or should not affirm.
The two uses of diabebaioomai in the Pastoral Epistles set up a contrast: false teachers confidently affirm things they do not understand (1 Timothy 1:7), while Paul commands Titus to confidently affirm trustworthy sayings about grace and good works (Titus 3:8). Confident assertion is not inherently virtuous — the content being asserted matters supremely. This is a perennial warning: religious confidence can be misplaced. True theological confidence flows from the gospel's 'trustworthy sayings,' not from human speculation.