Humble doesn’t counter abilities that have already triggered or been activated. In particular, casting this spell won’t stop a creature’s ability that says “At the beginning of your upkeep,” “When this creature enters the battlefield,” or similar from triggering.

Humble overwrites all previous effects that set the creature’s base power and toughness to specific values. Any power- or toughness-setting effects that start to apply after Humble resolves will overwrite this effect.

Effects that modify a creature’s power and/or toughness, such as the effect of Seal of Strength, will apply to the creature no matter when they started to take effect. The same is true for any counters that change its power and/or toughness and effects that switch its power and toughness.

If the affected creature gains an ability after Humble resolves, it will keep that ability.