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Francesco, Marquis of Saluzzo, was Francis I's lieutenant in Piedmont and owed much to the French crown. Frightened by widely circulated prophecies that Emperor Charles V would triumph and France would fall, he defected to the imperial side. The predicted outcome did not arrive, and he ruined his position and reputation by acting on the forecast rather than on his obligations and the actual state of affairs.
At Samothrace, Diagoras was shown the votive tablets hung by sailors who had prayed to the gods and survived shipwreck, as proof that prayer works. He answered that there were no tablets from those who prayed and drowned. The evidence for providence was assembled only from survivors, so it could not distinguish divine help from chance.
Anyone who shoots at the target all day will sometimes hit it, and almanac-makers and diviners produce so many predictions that some are bound to come true. People record and repeat the hits and quietly forget the far more numerous misses. Deliberately obscure oracles help this along, because interpreters can fit almost any event to them after the fact.
The same decision made on the same reasoning can produce opposite results, because fortune shares authority over every outcome. The sound approach is to deliberate carefully, act on your best judgment, and then evaluate that judgment by its reasoning rather than by how things happened to turn out. Under this rule, uncertainty is no excuse for paralysis, and a good result is no proof of wisdom.
Fortune regularly achieves what planning and skill cannot. Jason of Pherae had an abscess that doctors could not cure, and it was lanced by an enemy's sword in battle. Treating outcomes as fully controllable is therefore a basic error about how the world works.