Since it's kind of difficult to predict the results of the match because some unpredictable circumstance might occur during the game play time, a gambler can not be a hundred percent sure of his predictions when the game hasn't ended. This is why gamble is based on luck, although your skill might also help you achieve a winning but luck plays a big role in gambe which makes luck very important while you are gambling.
Indeed, even you did your research there are factors that can still affect the outcome, things that unforeseen when you place your bet, a good example if injuries happened during the game surely it affects the performances of the players or the team, it's something that can change the direction of the outcome.
There's no guarantee at you can assume and hope that with luck will be at your side after placing your bet.
Usually such luck is not only for gamblers but for the underdog team because they can get good chance from the mistakes of the favorite team, but things like this do not happen all the time and we as gamblers must be smarter in determining and considering the predictions of the results of the analysis carried out.
Luck in sports bet is just good fate for gambler when they choose what should not happen, you are right that there is no guarantee that anyone can get lucky after they place bet.