> If market followed rational logic, you could pre-calculate which stocks will be what price and never lose money.

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.

"(Stock) market is, by definition, irrational"

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.