The first is that there have been a series of favorable supply shocks that have temporarily lowered inflation, for a given unemployment rate, resulting in the appearance of a decline in NAIRU. In this case, absent further favorable supply shocks, inflation performance will not be as favorable for any given unemployment rate as we return to the historical relationship between inflation and unemployment.
Second, there may have been a longer-lasting change in the bargaining power of workers relative to firms and/or in the competitive pressure on firms that has resulted in unusual restraint in wage gains and price increases. One explanation in this genre is the “job insecurity” hypothesis and a second is the “absence of pricing leverage” hypothesis.