(Stock) market is, by definition, irrational. If you are scared of solvency, sell and hold money and/or gold.
The fundamentals are unpredictable, so even a perfectly rational planning (suppose such thing could exist) would lose money sometimes. Not in the long run, but long run doesn't matter if a single wrecked ship can wreck you.
I assume this is just your definition?
Is weather irrational, because you cannot calculate it?
Markets and weather are just too complex with too many unknowns to calculate it.