The alphabet has 26 letters. That are 26 chances to capture Taekwoon's heart or else Hakyeon promised not to bother Taekwoon ever again. There is a high risk that Hakyeon will fail, but if you have tried everything to asked your crush out and everytime got a negative reaction. This would be the last chance for Hakyeon to make Taekwoon fall in love with him. after all... nothing ventured, nothing gained.