If you just started playing and haven't kept records or you're not able to figure out how good your opponents are then you are just assuming you can beat them.
I can sit at a table and know what I'm facing by how they're playing in about 1-2 orbits but if you can't then some people have a poker tracker to keep track of their results against opponents or they let a HUD tell them how people are playing or you can go to a site that tracks
online poker results to see if your opponent have any success at the level you're playing.
It goes back to that saying "If you can't spot the fish. . . Meaning if you can't recognize who you are playing based on true knowledge/expericence of the game you are playing then you are going to be in trouble.
And the catch is if you're still losing after evaluating that your competition is weak then your believe of what a "good player" could be false or its something else that says you don't have the experience to beat them at that level like playing past your
bankroll or not thinking about the variance that's involved with your style/strategy against theirs.