Well, you understand little about the game if you can't beat random team near your quality with consistency.
Every option in the game makes a small difference, but they are not really critical deciding factor until that one day happen. Say if your captain bonus increase your chance of a shot made by 2%, it is only 1 in 50 games that it works. And that one additional shot isn't a deciding factor if you are already winning.
You could have done everything that increase your chance to win, but your chance could never reach 100%. Someday, the randomness will screw you up no matter what.
But, given when you have done everything in your ability to increase your chance to win, I can say you can win or draw 90% of the time against opponents with similar quality team. In fact, many experienced players have done exactly that especially f2p players who managed to reach the higher levels.