Study recommended for 21 kyu or stronger.(Show more of this level)
When black makes an ogeima shape with there remains a weakness in his shape.
White can easily abuse this weakness by playing . Black has almost no choice but to play the slow move of . When you look at the result it is clear that should have been played at immediatly.
Even when black tries to attach to with a kosumi shape this only strengthens white more. There still remains a weakness in his shape.