That's a more interesting question than you might have intended it to be. A designer's job has two contradictory aspects. One is knowing the rules and followin

That's a more interesting question than you might have intended it to be. A designer's job has two contradictory aspects. One is knowing the rules and following the rules. The other is having novel ideas, and breaking the rules when it works. The balance between those depends on the brief, and the designer's place in the ecosystem. For example the architect I paid to design my extension wasn't in the business having novel ideas - he designs well proportioned buildings in established styles, that work as living spaces, don't fall down, and get approved by planning authorities. But other architects are paid to design skyscrapers that look like nothing you've seen before. For a school fete poster, you're probably more in the first category - follow the rules. But you want to know where there's room for variety within those rules. Which is where the blog post starts - not every Spring fete poster has to have bunting and daffodils.