I come to understand that it is more worrisome when the sure winning opportunities was so huge and got lost lately closed to the end time of the game.
Gambling doesn't give anyone the assurance of winning, but gamblers assure themselves of winning meanwhile there is no guarantee of winning or losing a game. What you @OP is trying to describe happens frequently in gambling, especially in cases where, for instance, you place a bet between two clubs and perhaps you think that team A is stronger and will be able to beat team B. From the start of the match, it could be going as predicted, but in the last few minutes to end the match, you may just see the weak team winning the match and your bet gets burst.
You might feel bad, especially if it's a club you support that loose the game, but you might feel very bad if you actually assure yourself that you will win that game. It's not wise to assure yourself of winning a game because gambling is not something that winning is guaranteed at every bit.