Anecdotes are poisonous data, and it is best to exclude them from your reasoning when possible. They are subject to a massive selection bias. At best they are useful for inferring the existence of something, e.g. "I once saw a plesiosaur in Loch Ness.". Even then the inference is tenuous because all you know is that there is at least once individual who says they saw a plesiosaur. Inferring the existence of a plesiosaur requires that you have additional supporting evidence that assigns a high probability that they are telling the truth, that their memory has not changed significantly since the original event, and that the original experience was genuine.