There has been a long-running discussion as to whether infrared(IR)
quantum corrections can make (quasi-)de Sitter spacetime unstable. If
this effect is truly present, the increasing IR contributions might
affect on the dynamics of inflation. In this talk, I will explain the
origin of IR possibly unstable contributions and will discuss whether
these effects are physical or not. Based on this consideration, I will
also discuss cosmological implications of the long wavelength
fluctuations.