Favourable conditions on the rivers and streams I fish mean a day or so after some rain when the levels are dropping but running reasonably clear. If I turn up and it still looks like milky tea or hot chocolate then I don't bother. When it's 'on it's bones' and hasn't rained for ages it is harder, especially if the sun is high in the sky but those fish you do catch count extra. Also time spent in reconnaissance is seldom wasted! In the Spring until the Autumn the evenings are easier than the days.
Finally, when you are walking back to the car after a blank, conditions were obviously unfavourable.
You have to be in it to win it!
SharkeyP