Earlier quoted context omitted.
> A theory about a conspiracy is when outsiders to the conspiracy try to reason about motives without being privy to the actual motives (if any) of the conspiracy. By their nature, conspiracy theories can be far more wide ranging than the actual motives of any conspiracy will be. This is one of the things that makes conspiracy theories problematic. This seems like it would apply equally well to all theories.
Motives are a lot more difficult to reality check than are physical properties. Especially if, as ethanbond indicates, the person with the theory doesn't believe what the other people say about their motives.
And the conclusion you draw is fully general. There are more possibilities for why something happened than there are reasons for it. What are we supposed to have learned?
> Especially if, as ethanbond indicates, the person with the theory doesn't believe what the other people say about their motives.
The modal case is that, when someone makes a claim about their own motives, they are lying.
The second most common case after that is that they don't know their own motives and their reported motive is not accurate.