Flourishing is properly the main human end, and flourishing is activity of soul that succeeds in accord with virtue.

When I accept someone's testimony, I am thus only a small part of the full seat of epistemic competence, which might include many others in a long chain. My own contribution might then be slight, just through the perceptual and linguistic competence involved in knowing what someone is saying or writing, etc.

When the risk of failure is too high, the right choice is to forbear.

If the agent aims to make the attempt if and only if it would be apt, then a distinctive element of risk assessment becomes relevant: How probably would the agent succeed in attempting that fuller end?

Success is better than failure; an attempt is a better attempt, it is better as an attempt, if competent than if incompetent; and it is better to succeed through competence - aptly - than through sheer luck.

It is bad to want something that not even God could attain, especially when the impossibility becomes obvious.

The risk pertinent to a particular attempt (and to its evaluation as an attempt of its sort) is the risk that the agent will fail to attain the end constitutive of that attempt. This risk of failure is coordinate with how likely or unlikely it may be that the agent will then succeed.