Start with a pencil

The trap of pixel-perfect mocks

You’ll make a better design if you avoid pixel-perfect mocks while you’re still deciding what to do. Why? Two problems: First, if you gloss a weak idea with finished-level polish, you’ll fool people into thinking your initial (but seemingly visually perfect) sketches are your final, thoughtful designs; Second, you risk seducing yourself into hanging onto a weak idea for too long because you’ve put a ton of effort into making it visually perfect (even if it’s conceptually unsound).

More here:

https://medium.com/design-story/start-with-a-pencil-a68ff0dd37e