If you are so confident that Liverpool will win, then you should place a bet - an easy +61% is a very good return on one event. But don’t forget that this season Liverpool have already lost points twice (more precisely once, and the second time they were knocked out of the Cup) in games with United.
I also really want to place a bet and I will be sorry to miss the opportunity (like yesterday when the City victory odds were 1.54 after the first half) but I will wait for a more reliable situation.
I got your point.
You can be confident but you can not be sure about result.
Even with yourself, you can not be sure what you will get from what you do. There is possibility for uncontrollable things and with a football match, there are many factors for uncontrollable things. It's not only about you, a single person, but about dozens of people: 22 players from two squads, 2 head coaches, some substitutions, 1 referee and other assistant referees. You surely can not control all of those factors so nothing to be sure with result of a match and your bet.
Seoarate fluctuations do not change the overall picture. The most important thing is whether the bet is profitable or not, this is what you need to be confident. Because if you always make only profitable bets, then in the long run you will be in the black. Let me give you an obvious example: let’s say you can bet on any City opponent with odds of 30. It is clear that you will lose 80% or even more of your bets, but the outcomes that will be in your favor will compensate for the losses and bring profit.