"Now Jacob took for himself rods of green poplar and of the almond and chestnut trees, peeled white strips in them, and exposed the white which was in the rods. And the rods which he had peeled, he set before the flocks in the gutters, in the watering troughs where the flocks came to drink, so that they should conceive when they came to drink. So the flocks conceived before the rods, and the flocks brought forth streaked, speckled, and spotted. Then Jacob separated the lambs, and made the flocks face toward the streaked and all the brown in the flocks of Laban; but he put his own flocks by themselves and did not put them with Laban's flock. And it came to pass, whenever the stronger livestock conceived, that Jacob placed the rods before the eyes of the livestock in the gutters, that they might conceive among the rods. But when the flocks were feeble, he did not put them in; so the feebler were Laban's and the stronger Jacob's. Thus the man became exceedingly prosperous, and had large flocks, female and male servants, and camels and donkeys" (Gen. 30:37-43).
Admittedly, this section of text is confusing to our modern way of thinking. Why would Jacob peel white strips in tree branches and make sure the flocks could see them when they were in heat? The answer: It was believed in that era that whenever an animal conceived its offspring would bear the mark of whatever it was looking at! So, essentially, based on what the text reveals, we have Jacob (again) trying to "help God" via dishonorable behavior. Jacob is going to try to cause the flocks to bear lots of speckled and spotted offspring since they would be his (and since Laban had not been very honorable toward him)! I cannot help but wonder if Jacob's behavior here is mostly retaliatory and whether he would have done such had Laban had been more fair and honest (cf. 31:7,8). Regardless, his plan is successful and he becomes wealthy very quickly. But we must ask: Why was he successful here? Was it because of the techniques he employed? No, though they appeared to be working for him. Ultimately, he was successful because God blessed him! God saw to it that an unusually high number of speckled and spotted were born to the flocks Jacob was tending to. I believe this would have happened without Jacob trying to "help" via behavior that Laban, at the very least, would have considered shameful (though Laban himself is not very noble either, as we have seen and will see again).