1. A system for a vehicle, comprising: a head-up display; and a circuit, which is connected to the head-up display, wherein the head-up display is configured to project an image onto a front windshield of the vehicle or onto a separate combiner, wherein the circuit is configured to output image data to the head-up display in order to generate the image, whereby the image data has a set of objects which includes messages for a user, wherein the circuit is configured to determine a user's workload level for operating the vehicle, based on a set of driving conditions, the set of driving conditions including at least a road situation, wherein the circuit is configured, based on the user's workload level, to switch between at least one first workload mode and a second workload mode, whereby the second workload mode is assigned a higher user's workload level than the first workload mode, wherein the circuit is configured, in the second workload mode, to reduce at least one object, which is output in the first workload mode such that a combined user's workload comprising the user's workload level for operating the vehicle and a user's workload for comprehending a content of the image is reduced in the second workload mode as compared to the first workload mode, and wherein, to reduce the at least one object, the circuit is configured to make the object in the image smaller, or to increase a transparency of the object and fade out the object.