The bolded part is where most people make the mistake when gambling. They 100% know in their heads that the sports team they are about to bet a house on is going to win, but then that team that they were so confident in loses and they are now ready to commit suicide.
People aren't considering the fact that sports can be rigged, injuries can happen, a guy can get ejected from the game, or whatever. You're not factoring in random bs. SO why risk big? Keep betting small and growing your money slowly, if you lose then you still have money left to rebuild from that loss.
Rigged matches certainly happen, but I'm not that knowledgeable to know much details. There are multiple times that the match I was considering "safe" doesn't have the outcome I was anticipating, and sometimes it's ridiculous too. I remember it was a match where Olympiakos lost to Panserraikos, in the Greek Super League. There's no way in hell they lost to Panserraikos, unless it was fixed, or all of their players had a brainfreeze for the whole match.
I usually bet on the weekends, from Friday to Sunday, I can afford betting on more matches or with higher amounts, or both, however, I don't want to be bashing my head when I lose, because it'll happen eventually, and it would suck losing $100's when this money could have gone for the electricity bills etc. Playing on the safer side is much better, and more entertaining, you have peace of mind.