*Limitations*

There are several limitations of this study. A sample of only women was used in the study. To determine whether the same effects occur in men, additional research should be conducted to examine whether practicing acts of kindness can affect materialism by improving life satisfaction. A similar concern applies to age and education: given the high homogeneity of our sample, future research should be designed to replicate this study with participants of different ages and educational backgrounds to generalize our results to more heterogeneous populations. Second, the control task in the study seemed to increase the participants' life satisfaction; for this reason, it may not be neutral. Future studies should consider the use of a control condition in which the participants do not perform any activity (the so-called passive placebo), with changes in well-being over time simply monitored. Third, since some of the significant results of this study had small effect sizes (e.g., the effect of kindness on affiliations), caution is needed in their interpretation as well as replication in future studies. Furthermore, future studies could control for whether practicing acts of

kindness contributes to an increase in kindness—in our study, we only measured kindness as a trait at pretest to check if there were differences between study conditions. Finally, our study results could be affected by specifics of culture and economic status of the country where the study was conducted (i.e., Poland).
