We studied the role of the illusory perception of the size of a target in the effectiveness of shooting it. Three groups with equally good shooting skills were required to shoot targets on a wall 1.5 meters away. During the training session, the target size was 46 × 39 mm for both the experimental group and control group 1 and 33 × 39 mm for control group 2. The target for the experimental group looked smaller because it was included in a modification of the Ponzo illusion. During the subsequent test session, the target size for all groups was 33 × 39 mm. The experimental group participants were the least accurate during the training session. There were no differences between the experimental group and control group 2. During the test session, control group 1 was the least accurate. This suggests that the lines of the Ponzo illusion acted as distractors for the experimental group, but the illusory diminishing of the target had an additional effect on the experimental group’s shooting abilities due to training on a smaller (real or illusory) target. These results suggest that the illusory size of the target plays an important role in the accuracy of shooting and that by changing the illusory impression, not the reality, we can change the effectiveness.