When users fill out a form, they must type or select their input. All you need to provide is a text field to allow input typing. But to enable input selection, there are many components to choose from.
As a designer, you have to decide the best component to use and how to design it optimally. A common mistake is to rely on native form controls such as radio buttons and select menus to do the job. These native controls have usability issues that require a high cognitive load to make a selection.
Touchability and Fidelity
Native controls are hard to touch because they have smaller touch targets. When users use their finger to select input, they need larger targets for accurate touching. Small target sizes are passable on desktop devices but problematic on mobile devices.
Secondly, native radio buttons and select menus are designed for low information fidelity. As a result, users don't have sufficient info to make the correct selection. They have to think more about each option before they can act. Sometimes if they can't tell the difference between options, they'll either make a guess or abandon the form.