You get lower gearing (~34x28) and learn to take longer routes so that the grades are more manageable. Spread the 37% grade across 4x times the distance, and you're at 10% average which is painful but doable. You rarely see people cycling on hills like that. For example, in SF you can get around a large fraction of the city with only modest hills, plenty of people get by on fixies. There's always the mountain bike approach, which is to just get off and walk the bike. On a hill that steep, it's probably faster anyway.