Why is it important to plan out the design of an app?

you could mess it up

Explanation:

let me explain an app may be easy if you know what your doing. if you dont you most likely might miss a code or mess up the hole code.

only #2 represents an object at rest on a table.

in #1, there is no normal force due to the table; the object is accelerating downward.

in #3, the vertical forces are not balanced; the object is accelerating downward.

in #4, neither the vertical nor the horizontal forces are balanced. the object is accelerating upwards and to the right.