The phrase "how is that possible" is used to express surprise, disbelief, or curiosity about how something can happen or be true. It questions the feasibility or plausibility of a situation or event. It typically seeks an explanation or confirmation that what seems unlikely or unexpected can actually occur. This phrase often implies a reference to a specific situation that has been mentioned or observed. For instance, one might say, "How is that possible?" when encountering something astonishing or seemingly contradictory, asking for an understanding of the mechanism or reason behind it. In summary, "how is that possible" means asking for an explanation or reason behind something that appears surprising or difficult to believe.