The Ritt and Kreiss resolvent conditions are related to the behaviour of th
e powers and their various means. In particular, it is shown that the Ritt
condition implies the power boundedness. This improves the Nevanlinna chara
cterization of the sublinear decay of the differences of the consecutive po
wers in the Esterle-Katznelson-Tzafriri theorem, and actually characterizes
the analytic Ritt condition by two geometric properties of the powers.