An embodiment proposes a method for performing wireless communication by a first device. The method may comprise the steps of: selecting a first resource within a first selection window on the basis of first sensing; generating a first medium access control (MAC) protocol data unit (PDU) on the basis of at least one logical channel (LCH) in which hybrid automatic repeat request (HARQ) feedback is enabled; transmitting, to a second device, first sidelink control information (SCI) for scheduling a first physical sidelink shared channel (PSSCH), through a first physical sidelink control channel (PSCCH), on the basis of the first resource; and transmitting, to the second device, second SCI and the first MAC PDU, through the first PSSCH, on the basis of the first resource. For example, random selection of the first resource may not be allowed on the basis of the at least one LCH in which the HARQ feedback is enabled.