I’ll answer with a simple test. Do the following first on your phone and then on a piece of paper:
Design a thing, something physical; a box, a house, a chair, whatever. In addition to the diagram, this note must include a description of the item, the bill of materials, the dimensions and, if applicable, assembly instructions that you could confidently hand to someone else and have them follow. Ideally, you should include the dimensions of the object directly on the sketch itself.
Now give this to someone and see how accurately they can reproduce the item while you go off and make a phone call.