Do confident people say probably or could be?

Of course. People who think only in terms of the absolute, such as always or never, tend to be overconfident or even arrogant.

We say what we want!

They say "definitely."

Probably.

It depends upon the subject. Confident people also have the confidence and courage to know when something is not absolute and to abide by that knowledge.

It all depends. People think absolute, definite, certainly sure(always never) tend to be over-confident or (arrogant).
I now confident this answer works.

They say absolutely.

Either one

I don’t know I’m not a confident person

The concept of self-confidence self-assurance in one's personal judgment, ability, power, etc. Social psychologists have found self-confidence to be correlated with other psychological variables within individuals, including saving money,[18] how individuals exercise influence over others,[19] and being a responsible student.[20] Marketing researchers have found that general self-confidence of a person is negatively correlated with their level of anxiety.[21]
Some studies suggest various factors within and beyond an individual's control that affect their self-confidence. Hippel and Trivers propose that people will deceive themselves about their own positive qualities and negative qualities of others so that they can display greater self-confidence than they might otherwise feel, thereby enabling them to advance socially and materially.[22] Others have found that new information about an individual’s performance interacts with an individual’s prior self-confidence about their ability to perform. If that particular information is negative feedback, this may interact with a negative affective state (low self-confidence) causing the individual to become demoralized, which in turn induces a self-defeating attitude that increases the likelihood of failure in the future more than if they did not lack self-confidence.[23][24] On the other hand, some also find that self-confidence increases a person's general well-being[25][26] and one's motivation[27] and therefore often performance.[28] It also increases one's ability to deal with stress and mental health.[29][30]

https://en.wikipedia.org/wiki/Self-confidence

Knowledge and Its Limits

https://en.wikipedia.org/wiki/Knowledge_and_Its_Limits

http://www.asparkstarts.com/the-limitations-of-knowledge/