There is such a thing as a close but clear fight. People saying things like Pacquiao robbed Marquez annoy me because both fights were ridiculously close. Either way they went, the winner deserved it and the loser was unlucky.
If Boxer A clearly won at least 6 rounds and lost on 2 cards, there's reason for dispute, but all it takes is for 2 judges to see 1 more round for Boxer B rightly or wrongly and he has the split decision. If its a draw, both just have to suck it up and accept these things happen. For me, crying robbery sounds as if people are saying a fighter was twisted out of a clear win by poor or otherwise influenced judging. If a fight is (hypothetically) 6-5-1 in rounds, and it ends up a draw or split decision for the Boxer who (hypothetically) won 5 rounds, it is a close fight with what we see a clear winner, but if that boxer wins 1 of 2 cards and loses the SD, you cant really shout robbery. Unless of course the other 2 judges had it wide for the boxer who is generally perceived as the loser, then of course you have to ask who the hell was scoring the fight.
It depends on the fight, A closely scored fight like oscar vs trinidad or huck vs lebedev are robberies, pac vs marquez or williams vs martinez 1 are close fights that could go either way then you just need to be lucky to get the win.
If you win by a even just a point clear enough for a majority to think so, you deserved to win. I know boxing is subjective but that shouldn't be an excuse for incorrect calls within small margins to go unnoticed or excused. They can, and have, altered entire careers.