Why are indifference curves convex to the origin in economics?

The
indifference curve is convex to the origin because you receive less satisfaction for consuming
increasingly large quantities of something. Essentially, it is the concept of diminishing
returns. If you are hungry and you eat one cookie, the difference in pleasure will be massive
between receiving nothing and receiving one cookie. However, you will receive a smaller
difference in pleasure by receiving a second cookie and an even smaller difference for each
subsequent cookie.

Essentially, as you consume more product, your marginal
pleasure decreases, because the difference is less substantial...