Why does the universe's 'worst prediction' demand a multiverse?

The cosmological constant—Einstein's term for the energy of empty space—is theoretically predicted to be vastly larger than observed, a discrepancy of 120 orders of magnitude that many physicists consider the worst prediction in science. One proposed fix is the multiverse: if countless universes exist with different constants, we simply live in one compatible with life. The catch is that an infinite multiverse makes clean predictions almost impossible, a problem called the measure problem of eternal inflation.