When faced with a difficult decision, it is better not to take unnecessary risks. Also when in doubt, abstain and when in doubt, leave it out

Characterized by or experiencing no doubt at all, certain; undoubted; undoubting. / (obsolete) Free from fear or suspicion.

Without doubt; very probably, in all likelihood; doubtlessly.

In a doubtful manner, in context of doubt or ambiguity, questionably.

(sometimes proscribed) Without question; indubitably. / (obsolete) Without feeling doubt, without misgivings.

In a doubting manner.

plural of doubter

One who doubts.

(uncommon) Capable of being doubted; doubtful; dubious; dubitable. See usage notes below. / (obsolete) Fearsome; redoubtable.

the property of being doubtless