Doing a good research can increase the odds of winning, but it seems your friend thinks that it should guarantee a win, something that is impossible as anything can happen during a match and an underdog can always obtain a win through a weird series of circumstances happening during that specific match, and if he does not understands this then I do not understand why he makes sport bets, as analyzing the matches is almost the whole point and the most enjoyable aspect of sport bets.
It's true. By doing a research he is going to use some factors as hypothesis in order to justify his prediction, but these are still hypothesis, which can be confirmed or not through the match's results. In every cases, he is still launching some guesses, like for an example: to say a team is going to win, because the key player of the opposite team is injured. It does make sense to think like that, but the other players can still do a good job without having the key player on the field.
The variables are just too many to be analyzed accurately by gamblers. At same time, to place a bet based on an analysis is better than placing a bet based on nothing.