Reference
There is rarely one guaranteed solution. Use these clues to investigate, then adjust one variable at a time.
Possible causes include over-extraction, grind that is too fine, contact time that is too long, overly hot water or excessive agitation. Try grinding slightly coarser, shortening contact time or pouring more gently. If the ratio is very strong, reduce the coffee dose or add water after brewing.
Sourness can suggest under-extraction, especially if the cup also feels thin or hollow. Try a slightly finer grind, a longer brew time, warmer water or more even wetting. Some coffees are naturally bright, so compare sourness with overall sweetness and balance.
Weak coffee may come from too little coffee, too much water or low extraction. First check ratio. If the ratio is sensible, try finer grinding, longer contact time or improved agitation. Avoid making every change at once or the cause will remain unclear.
If the cup is simply intense, use less coffee, more water or dilute after brewing. If it is strong and harsh, extraction may also be high, so try coarser grinding or shorter contact. Strength and extraction are related but not identical.
Muddiness may come from excessive fines, a grind too fine for the filter, a damaged filter, aggressive stirring or pressing too quickly in immersion brewing. Try coarser grinding, gentler movement, more patient filtration or allowing the brew to settle before pouring.
Inconsistency often comes from changing several variables unintentionally: different water amounts, uneven grind, variable pouring, skipped preheating or different coffee freshness. Measure repeatably, use a timer and keep notes until your routine stabilizes.