What is the effect called on humans when
When you have seen series of bad events happen to you, and then the next tend to overvalue an negligible good thing happening as a gratitude or grand success or preciously value it
Similarly
When you have seen good events (things) happening to you, you tend to over-exaggerate (have negative effect for) an negligible negative thing happening as a insult or grand failure (you just can't digest it)
Overvaluing the last (most recent) effect is recency bias.
Wikipedia: Recency bias is a cognitive bias that favors recent events over historic ones. (https://en.wikipedia.org/wiki/Recency_bias)
This is called the contrast effect.
From Wikipedia:
A contrast effect is the enhancement or diminishment, relative to normal, of perception, cognition or related performance as a result of successive (immediately previous) or simultaneous exposure to a stimulus of lesser or greater value in the same dimension.
You are describing a Cognitive Bias, as described in Thinking, Fast and Slow by Daniel Kahneman.
One of the biases is called Loss Aversion.
Loss Aversion
Say you’ve just lost $50 gambling but have a 50% chance of winning it back, you would be more inclined to try again. Because you’re already in $50 deep. This is how many people get sunken into gambling loopholes.
(Source: Cognitive Biases to Watchout For — Thinking, Fast and Slow)
If you've had a series of good events, your loss aversion exaggerates the effect of the loss. (It is also called loss aversion when you exaggerate the effect of a gain after a string of losses.)
Selective memory (n).
Confirmation bias, the tendency to search for, interpret, favor, and recall information in a way that confirms one's preexisting beliefs or hypotheses. Wiktionary
The tendency to remember only what one wants to remember m-w
This is because the memory we have stored in our minds about the event is strictly based on selective memory in both good and bad times. Selective memory allows us to remember certain parts of the event that has happened in the past and put aside the ones that are not so important to us. Belinda Liau; True Leaders, Part III
It is to say that human memory is fallible. Events and people are remembered differently from the way they perhaps were, actions take on coloration, good and bad, and wishful thinking and selective memory play tricks. John Pen La Farge; Turn Left at the Sleeping Dog
