Contrary to the law of less work, individuals with high levels of need for cognition and self-control tend to choose harder tasks more often. While both traits can be integrated into a core construct of cognitive effort investment (CEI), the underlying mechanisms behind this tendency remain unclear. A plausible explanation is that these individuals intend to avoid the feeling of boredom during easy tasks. If this were the case, they would be less likely to increase their effort based on expected payoff, but rather based on increasing demand. In the present study, we aimed at measuring effort exertion objectively: the N2 amplitude derived from electroencephalogram has been found to be more negative and pupil dilation to be larger for higher cognitive demand. In a sample of N = 147, we examined the relationship of CEI and N2 amplitude and pupil dilation during a flanker and a n-back task with varying demand and payoff. In both tasks, indices were sensitive to demand and partly payoff. However, we neither found a main nor an interaction effect for CEI regarding N2 amplitude and pupil dilation. Taken together, our results do not support the notion that individuals with high levels of CEI exert less effort and exert it regardless of payoff. This may further our understanding of the conditions under which person x situation interactions occur vs. the conditions under which situations determine effort investment in goal-directed behavior more than personality, and vice versa.