Actually, a good strategy does work all the time if by all the time is meant all the time the trade set-up is correct.
So, a trend-following strategy produces profits when the set-up says follow this trend and you follow it and it continues. But a percentage of trends stall or reverse: the strategy says either hold on or get or let your stop-loss be hit - none of these occurring means the strategy has failed.
But the trend-following strategy also has a rule that if the trend set-up isn’t in place, you don’t take the trend. If a trend doesn’t occur in the market you’re looking at, that also does not mean the strategy has failed.
A strategy that fails when the market and chart behaviour in TA terms is identical was actually a poor strategy and was only profitable on a random basis. Even a high risk strategy can give a string of good returns, either because its been curve-fitted to a particular narrow scenario or, yes, due to the law of averages - even a trade based on a coin-toss will for some time definitely produce win after win.