While testing it’s easy to fall foul of logic errors in your thought processes. One of the most common errors is the post hoc fallacy.
This is a logic error or fallacy of post hoc, ergo propter hoc (after this, therefore because of this). It can sometimes be all too easy to attribute issues to unrelated events just because they follow them.
For example, a new tenant moves into a new flat and upon arrival the flats hot water boiler goes faulty. The landlord automatically assumes the arrival of the new tenant caused the fault. This is an example of the post hoc fallacy.
In testing we must resist the urge to jump to conclusions, and instead use investigation, logic and critical thinking.