Bond investors face the crucial decision of just how much risk to take in Treasuries with 10-year yields at the highest in more than a decade and the Federal Reserve signaling it’s almost done raising rates.

Investors loading up on long-term bonds have a history at their back.

The bond market’s re-energized bulls may want to dial down their excitement because their fortunes hinge on whether an abstract, almost elusive number, is as low as they assume.

When March’s bank failures ignited a historic bond rally, few, if any, made more money than Josh Barrickman. His army of funds gained roughly $26 billion, the equivalent of more than $1 billion in paper profits every single trading session.