My tea is bitter
The cup is harsh and sharp while it is in your mouth, and you want to stop drinking it.
Likely cause
Water too hot, in most cases. Caffeine and the bitter catechins extract much faster as temperature rises, so ten degrees does more than ten seconds. A cup left to cool while you were busy also reads as more bitter than it did hot.
Try this now
Brew the same leaf again at about eighty degrees, everything else unchanged, and taste the two together.
What to change
Drop the temperature first. If it is still harsh, shorten the steep. If it is harsh and thin, use more leaf for less time rather than less leaf for longer.