Well, maybe. But we aren’t there yet.

Total deposits in eurozone banks were 327 billion euros higher in October 2015 than they were when the negative rate policy was introduced in June 2014, and show relatively consistent growth in percentage terms both before and after the move below zero. Rates are even more negative in Switzerland, where the Swiss National Bank is aiming for rates as low as negative 1.25 percent.

One way to think of what is happening right now is as a grand experiment of “how low can they go.” Mario Draghi, the E.C.B. president, pointedly avoided answering questions at his news conference Thursday about whether the central bank had now arrived at its true lower bound, insisting only that the new negative 0.3 percent rate was appropriate right now. In other words, further cutting hasn’t been ruled out.

The flaw in the old concept of the “zero lower bound” seems to have been this: There are a lot of benefits to keeping money in a bank besides the interest you earn. If you keep $10,000 in savings in a bank, and the bank gets robbed, you’re unaffected; the bank is on the hook for the losses. If you keep it in your freezer, theft is your problem. The peace of mind of having your $10,000 in a federally insured bank account and the ability to write a check to make a purchase or wire money to a family member are valuable. More valuable, it seems likely, than the $30 in annual costs that would apply if the Fed put in place the E.C.B.’s new negative 0.3 percent rate.

The experience in Europe over the last year — really the absence of some catastrophe with negative rates — helps explain why one Fed official argued at the central bank’s September meeting that American interest rates should also be slightly negative. (The official is unnamed in official projections, but Fed watchers believe it is Narayana Kocherlakota, the Minneapolis Fed president.)

What we’re learning from Europe about negative rates and the nonexistence of the zero lower bound is an exemplar for a lot of monetary experimentation over the last six years. Tools that existed as academic thought experiments a decade ago are now becoming standard-issue parts of the central banks’ policy tool kit. Strategies tried briefly by small countries like Denmark are embraced by the giants of the world economy.

In other words, we know a lot more now than we did a decade ago about what works in extreme monetary situations. It’s just too bad we had to learn these lessons the hard way — through years upon years of trial and error, with lots of economic suffering along the way.