When a firm acquires 100% of the shares in another firm and finances this acquisition with available funds, the debt level and return on equity of the two firms in combination goes up (under certain conditions). In three experiments, we empirically demonstrate that individuals intuitively think these variables become lower after the acquisition, contrary to what is actually the case. The findings stress the role of psychological processes in business valuation and accounting and are consistent with an averaging account of judgment under uncertainty. On this view, people's judgments of objects in combination are biased toward the average rather than the sum of the objects’ individual characteristics. The experiments also show that informing the participants of the accurate evaluations removes the bias. The third experiment reinforced these results by replicating the same pattern with a sample of “high-accounting literacy” participants who all reported formal university training in accounting. One takeaway of the study is that, in acquisition settings, investors potentially could base their assessment of firm value on false premises which in turn (at least in the short run) leads to a higher level of asset mispricing and a less efficient capital market.