i generally teach my students present tense (with action verbs) is for habits and routines eg. i always win at poker; past tense is for something that happened and is finished eg. i won at poker last night; and present perfect is for something that happened before now but the time doesn't matter so much eg. i have won a few times at poker.
now imagine a game has just finished and you won.
you can say "i win", "i won" or "i've won".
where does that leave the old tenses? and the old teacher?!