In for a penny, in for a pound

Once you've started something or made a small commitment, you might as well go all the way. If you're going to take a risk, take the bigger risk for potentially greater reward.

This British phrase from the 1600s refers to the old monetary system where a pound was worth 240 pennies. The logic was that if you're willing to risk a small amount (penny), you might as well risk the larger amount (pound) for better potential returns.