For things false lie so close to things true, and things that cannot be perceived to things that can, […] that it is the duty of the wise man not to trust himself to such a steep slope.

[Ita enim finitima sunt falsa veris, eaque, quae percipi non possunt, iis quae possunt […] ut tam in praecipitem locum non debeat se sapiens committere.]

Marcus Tullius Cicero (106-43 BC) Roman orator, statesman, philosopher

Academica, Book 2, ch. 21 / sec. 68 (2.68) (45 BC) [tr. Rackham (1933)]
    (Source)

(Source (Latin)). Alternate translation:

For falsehoods lie so close to truths, and "appearances" which cannot be perceived to those which can, [...] that the man of wisdom ought not to trust himself on such hazardous ground.
[tr. Reid (1874)]

False and true, and innapprehensible and apprehensible are so close to each other, [...] that the wise person shouldn't commit himself to such a precarious position.
[tr. Brittain (2005)]

So near is falsehood to truth that a wise man would do well not to trust himself on the narrow edge.
[Source]