Pick blank sheet of paper; draw something, anything... I bet you will do something mediocre.
Pick a blank sheet of paper; draw 2 arbitrary straight lines; now, draw a house using those 2 lines... I bet you will do something creative, more interesting than the previous one.
Our brains are very limited. I mean, they're extraordinary achievements of natural engineering but, in the end, a lot less powerful than we believe. They perform really bad in too broad problems.
Go to a restaurant, the menu has 100 different options: you get blocked and anxious.
Go to a restaurant, the daily menu offers 3 starters and 3 dishes. Decision is made in seconds and you can rest on the chair while the order is taken.
But most of our lives in the first world is lived facing open problems, where clarity and purpose is missing. Our day jobs are the perfect example. Broadly defined responsibilities in a changing environment interacting with other broadly defined jobs in order to get something done, not very clear what that is, apart from meeting a certain budget.
In order to manage ourselves in such an environment there is a precondition: set limitations. The only way to put our brains to produce something is to clearly define the problem we're trying to solve, and in order to do it, setting limitations brings focus and clarity. But setting limitations is an art that nobody teaches us. Those limitations will be rationally unnecessary, like those 2 lines in the sheet of paper, but are required in order to deliver something interesting. If you interact with others, setting arbitrary limitations for the sake of boosting your performance will be faced with stupor. Why the hell should we limit ourselves this way? And coming up with an argument against the limitation is so easy: "drawing two straight lines will prevent anyone from drawing a round-shaped house, which is arguably the most interesting type of house".
In my experience, one extremely effective way to set limitations is to come up with an inspiring metaphor. When you create an analogy between a broadly defined situation and a well known thing, people get immediately hooked to the concept and their brains just get it. If the metaphor is cool enough, not that many people will be willing to spot the arbitrary limitations that the analogy creates, which is the main weakness of the method.
Everytime I'm stuck, I try to find the metaphor that inspires me, creates additional constraints on the problem, and allows me to come up with a response. It is such a powerful tool that I believe it should be taught at schools.
Have a good weekend!