This presents an interesting problem for people who want Witchcraft to operate like a scientific experiment.
Perform ritual A.
Say words B.
Light candle C.
Receive result D.
Real life is rarely so cooperative.
You can perform exactly the same ritual twice and experience something completely different each time.
That does not necessarily mean one ritual succeeded and the other failed.
The circumstances were different.
You were different.
The weather may have changed.
Your mood changed.
Your expectations changed.
The season changed.
The place changed.
Even if everything appears identical, time itself has moved forward.
The old saying that we cannot step into exactly the same river twice applies beautifully to Witchcraft.
The water has moved.
And so have we.