Drawing symbols instead of observed things
Beginners draw poorly because they draw their stored mental symbol of an object, such as an almond-shaped eye or a stick-figure hand, rather than the shapes actually in front of them. The symbol overrides perception, so eye proportions, foreshortening and edges get 'corrected' toward what the mind expects. Improving at drawing means learning to notice and suppress the symbol so that visual information reaches the page unedited.