Romans says the Spirit helps believers in weakness, especially when they should not know how to pray as they ought. The Spirit intercedes according to God's will, so weakness does not leave God's people abandoned.
Romans 8 speaks about life in the Spirit, suffering, hope, and future glory. The Spirit's help comes in the middle of groaning and waiting, not as an escape from all weakness.
This gives comfort to readers who feel spiritually inarticulate or burdened. Romans teaches that God's help reaches even into prayer that feels incomplete.
A careful reading should not turn the verse into a formula for effortless prayer. Paul is describing God's merciful help within weakness, hope, and waiting.
Original wording based on Romans 8:18-30.