I wondered why my treatment did not start at the full dose

When I started reading about diabetes and weight-management medicines, I noticed that many treatments begin with a lower dose and increase over time.

At first I assumed the goal would be to reach the effective dose as quickly as possible, so I was curious why doctors often increase gradually instead.

Is the gradual increase mainly to reduce side effects, or are there other reasons? For people who have gone through dose adjustments, what helped you understand the process?