Here is the detail most readers miss. Jakob did not set the peeled rods in the troughs every time. Targum Pseudo-Jonathan explains that he brought them out only when the early, the prime, the strongest ewes were conceiving (Genesis 30:41).
The feeble ewes he left alone. The weaker animals conceived without any rods in front of them — and their offspring went to Laban. The robust ewes, the ones whose young would inherit their strength, saw the striped branches and brought forth streaked lambs for Jakob.
This was not only a miracle. This was also selective breeding of the most sophisticated kind, centuries before anyone drew a pedigree chart. Jakob concentrated the marked offspring among the healthiest bloodlines, while the weak gave birth to plain animals that stayed in Laban's column of the ledger.
The Maggid teaches: the righteous are not only honest, they are attentive. Jakob worked within the letter of his contract and, inside those letters, deployed every drop of wisdom heaven had given him. Attention itself is a form of devotion.