Final answer:
The indifference curve is convex because the principle of diminishing marginal utility implies consumers get less additional satisfaction from each additional unit consumed, making the curve steeper on the left and flatter on the right.
Step-by-step explanation:
The indifference curve is convex or bowed inward due to the principle of diminishing marginal utility, implying that as a consumer acquires more of one good, the additional satisfaction (marginal utility) derived from another unit of that good decreases.
This assumption leads to the curve being steeper on the left and flatter on the right. Due to this curvature, the marginal rate of substitution, which is the rate at which a consumer is willing to substitute one good for another while keeping the same utility level, declines as the consumer moves down the curve. Hence, the marginal utility of one good decreases faster than the other, explaining why the indifference curve bows inward from the origin.