It is more difficult to climb a vertical staircasethan a slanted one give reason

The reason is similar to the reason why it is difficult to roll an object on a surface with a positive incline than rolling it on the ground

The more the path becomes vertical, the more force we have to apply to oppose the force of gravity

but when we are moving horizontally, we don't have to move against the gravity and hence, it is less difficult than going vertically upwards