Why are the three most simple alcohols completely miscible?
This happens because the intermolecular forces between different low molecular weight alcohols are very similar; as you say, they are dominated by hydrogen bonding. You can consider mixing on a molecular level to involve exchange of molecules from the two phases at their interface; if the energy changes involved are very small, mixing will occur as it is entropically favoured (mixed phase is more disordered) and the average thermal energy is far higher than the barrier to diffusion.