A psychologist friend has grown obsessed with finding individuals who exhibit extra-sensory perception (ESP) using a simple test: a "sender" individual looks at a card showing one of two possible shapes and concentrates very hard on the image while a "receiver" individual identifies the shape (without looking at it). Being a careful scientist, your friend randomizes the pairing of sender and receiver as well as blinds the experimenter, so there is no opportunity for signaling to the receiver using normal senses. Assuming that ESP-capable individuals would be very rare and since your friend's time is finite, they decide to test many people with relatively few cards each, as opposed to testing relatively few people with many cards each. After testing several thousand pairs of people with 10 cards each, your friend analyses the data and excitedly informs you that several individuals perfectly identified all 10 cards! Why is your friend's excitement (probably) unwarranted?

If your friend had decided to test relatively few people with many cards each (10), what might this strategy be able to detect that the previous strategy could not?