Why does Zeus let poseidon make Odysseus' journey difficult?

Zeus allows Poseidon to make Odysseus' journey difficult because he respects Poseidon's authority as the god of the sea and recognizes the validity of Poseidon's anger towards Odysseus for blinding his son, Polyphemus. Additionally, Zeus understands the importance of trials in shaping Odysseus' character and ultimately leading him to growth and wisdom. By permitting Poseidon's interventions, Zeus ensures that Odysseus' journey remains challenging and transformative.