sMON represents a share of the total pool of staked MON. The staked MON
earns yield over time in the form of more MON, so the amount of MON in the
pool grows relative to the amount of sMON outstanding. As this happens, each
sMON token represents more MON in the pool — holding sMON gives you both
your initial stake and your share of the yield earned since. This ratio
never resets to 1:1, so the value of sMON relative to MON grows continuously
over time.