Retracement beyond 61.8% of the preceding wave and it acts a good point for risk management. Trend invalidation doesn't happen till the time wave low/high is broken, but if the 61.8% mark is broken probability that wave low/high is going to break increases.
Gold (XAUUSD)- 3rd is extending. 3(green) of 3(white) looks complete and a correction in 4 of 3 is due. Since 2 of 3 was deep in a zig zag 4 of 3 should be shallow and may form either a flat or a triangle. 1838 is 38.2% of the rise and the spot price should ideally not fall below that.