Take true statement but invalid converse
eg. lamp is broken so the room is dark, room is dark and so the lamp must be broken
An example would be:
Involuntary celibates are lonely
David is lonely
David is involuntary celibate.
Or
Socially isolated people are lonely.
Sarah is lonely.
Sarah must be socially isolated.
But if the first two are propositions (things you know are true) you can make the third conclusion based on the first two as it affirms the consequent, there are other possible causes for the minor premise (Sarah is lonely). It is illogical.
So you are taking the end result and applying the wrong cause that isn’t necessarily linked to it.